I think I'm worried that science will _not_ advance exactly as it did last time. Right now we have two things: a) the technology to create the physical medium of the message and b) the technology to encode it in a way that is efficient in terms of its storage.
Who's to say that future generations will have both (a) and (b) at the time they come across the message? If they don't, then either they will not recognise it for what it is, or they will not be able to read it, or both.
>> they'd still leap forward 200 years in whatever they find.
Even if there's no collapse, I assume the future will like to know a few things about the past, but of course we can't know. Maybe the future is a boot stepping on a human face, forever and such things as history are not allowed. That would be a development entirely unrelated to technological means, but that would defeat any planning based on assumptions about future technologies. And unfortunately we can't really do much about it except, I don't know- form secret societies for the preservation of knowledge? Like in Nightfall [1]? :/
[1] https://en.wikipedia.org/wiki/Nightfall_%28Asimov_short_stor...
Take our plane, rocket and nuclear technology, would it be as advanced relative to other sciences if WW2/the cold war hadn't have happened? If a lot of money and manpower hadn't been ploughed into it relative to other sciences for 30 years?
Also this preservation technology is now available to us going forward, say a catastrophic collapse happened 200 years from now and 2000 years from now they get the technology to decode these things, they'd still leap forward 200 years in whatever they find.