When Seth refers to life-plans, he is referring to individual life-plans:
“Consciousness forms the genes, and not the other way around, and
the about-to-be-born infant is the agency that adds new material through
the chromosomal structure. The child is from birth far more aware of all
kinds of physical events than is realized also. But beside that, the child
uses the early years to explore — particularly in the dream state — other
kinds of material that suit its own fancies and intents, and it constantly
receives a stream of information that is not at all dependent upon its
heredity or environment.
On these other levels the child knows, for example, of its con-
temporaries born at about the same time. Each person's "individual" life
plan fits in somewhere with that of his or her contemporaries.
Those
plans are communicated one to the other, and probabilities instantly are
set into motion in Framework 2. To some degree or another calculations
are made so that, for instance, individual A will meet individual B at a
marketplace 30 years later — if this fits in with the intents of both
parties. There will be certain cornerstone encounters in each person's life
that are set up as strong probabilities, or as plans to be grown into.”
(The Individual and the Nature of Mass Events)
In other words, if individual A meets individual B, and the two eventually enter a marital relationship, the implication is that the life-plan of A meshed with the life-plan of individual B, and their meeting may well have been planned many years ago before they entered physical reality.
Seth's use of the term “blueprint” is a bit different to the meaning he gives to life-plan. The word blueprint occurs 36 times in The Unknown Reality, Book 1, so it seems to be an important concept.
"Each probability system has its own set of “blueprints,” clearly defining its freedoms and boundaries, and setting forth the most favorable structures capable of fulfillment.
These are not “inner images of perfection,” and to some extent the blueprints themselves change, for the action within any given system of probabilities automatically alters the entire picture, enlarging it. The blueprints are actually more like inner working plans that can be changed with circumstances, but to some extent they are idea-lizations, with a hyphen. As an individual you carry within you such a blueprint, then; it contains all the information you require to bring about the most favorable version of yourself in the probable system that you know. These blueprints exist biologically and at every level — psychically, spiritually, mentally. The information is knit into the genes and chromosomes, but it exists apart, and the physical structures merely represent the carriers of information. In the same fashion the species en masse holds within its vast inner mind such working plans or blueprints. They exist apart from the physical world and in an inner one, and from this you draw those theories, ideas, civilizations, and technologies which you then physically translate" (from "The “Unknown” Reality, Volume One (A Seth Book)" by Jane Roberts, Robert F. Butts, Session 696)
Kindle edition:
https://amzn.eu/dVQLLyoFrom the above quote it is apparent that the species as a whole (our human race) operates according to certain blueprints, and each individual also has their own blueprints. Seth also says that blueprints can be changed with circumstances, meaning that they are NOT deterministic.
Seth also makes an interesting connection between one's private blueprint, illnesses, and epidemics:
"
The private blueprint, yours at birth, is in certain terms far greater than any one physical materialization of it that could occur in your space and time. This provides you with areas of choice, gives you manipulability, and allows for the myriad of probable activities “possible.” You are the judge and the final word in that regard, so that as your ideas change, as you move toward one probable self and decide upon that as your official3 self, you will always have a rich bank of probable actions to choose from. If only one were provided you would have no choice. The same applies to the species. Your current decisions to accept one specific line of consciousness as real, and to ignore others, makes such concepts difficult to understand. You train yourselves — biologically, even — to inhibit certain stimuli, yet often the body itself responds to the very stimuli that you consciously ignore. By opening up your minds to new kinds of significances, however, you can begin to glimpse other orders of events4 with which you are quite intimately concerned. Often, for instance, you handle probabilities very well, while remaining consciously blind to them because of your concepts. Even then, however, on other levels your unconscious reaction will follow your own conscious intents. You may make a move in physical life, for example, seemingly for one reason. You may also be unconsciously reacting to quite pertinent data regarding the probable actions of others. Because you do not really fully accept the fact that you can so react, you may block this unofficial information on the one hand, even while on the other you take it into consideration. You are far more aware than you realize of the probable future in areas with which you are concerned. This is true on all levels.
If your purposes do not involve illness, for instance, and yet if you believe in contagion, you will automatically avoid circumstances that can lead to epidemics. In terms of probabilities that particular kind will not enter your experience. Give us a moment … All of this applies en masse in terms of diseases, for example, that run rampant through a species." (from "The “Unknown” Reality, Volume One (A Seth Book)" by Jane Roberts, Robert F. Butts, Session 697)