I would not keep old curriculum just to prove what you did. I like the idea of keeping the scope/sequence page. I’m in a state that doesn’t require record-keeping. When my kids were in 8th and under, I generally just kept artwork or writings I couldn’t bear to part with, and a list of what we had done for each subject. Sometimes I kept my schedules for a year and then recycled them.
In High School, I kept a few more things:
a course description for each subject (often a paragraph copied & pasted from a curriculum website–I can always rewrite it later if I need to send it somewhere, but I have the info handy at least)
a list of all resources used–books read, movies watched, field trips/activities, etc…
a list of test scores and papers written. Usually their papers were on the computer, so I would have something representative to show if I needed to. If you have a scanner, you could scan a few things if you were concerned you might have to show something. Some people keep a portfolio with a sample from each subject, so that’s an option too.
Here’s one site on Texas record-keeping: https://www.thsc.org/home-school-resources/recordkeeping/
Other things you might not normally think of are things like immunizations. If you do any kind of standardized testing, keep those records. If you have kids who have done any kind of evaluation for learning disabilities, keep those (and if they haven’t been evaluated but you suspect disabilities, keep a record of ways that you accommodate them–it’s very helpful to have this later on, both as you seek an eval, and if you seek formal accommodations for standardized testing.)
Here’s what HSLDA says–this is more than I kept, but might give you food for thought:
https://www.hslda.org/earlyyears/Records.asp