I'm well acquainted with the revelation of, 'I forgot I had that!', bit usually it's 'dangit, I know I had that...now where is it?!?'
Yes, this is common practice with me. At least for the non-cataloged parts I still have to inventory.
One thing I learned fast when I started inventory management is that marking the box as to what was in it started to get very cumbersome, very quickly as I have some boxes with 50 parts in them, some with only 2. I then started marking the boxes with a number and having an inventory sheet for each box. If the part was too large and loose without a box, I would assign it "shop" or "closet" or wherever it is stored. Then I got the idea that it was becoming too much paper to keep track of and started the Excel spreadsheets.
If there's an NOS part to fit an 85 442, it's probably at least an 85% chance I have one. I've got a lot of 87 442 stuff too. But I don't have everything. I have peripherals and fasteners for the V8, but not the heads and block itself. Nor the transmission, frame, or rear axle assembly, but I have lots of individual parts for them.
There's also one little fact to consider when collecting NOS GM parts that over the years, the GM replacement part may not appear to be the same exact part that the factory installed. I will just have to deal with that. Maybe refurbish and reuse the old part if possible. A few things that comes to mind is the heater cutoff valve on the back of the intake is tough to find in its factory configuration. The banjo style diaphragms you can find everywhere weren't used on 85s at the factory. At least not in February of 1985 when my car was built. It has the plastic unit with the separate brass vacuum can attached to the side, similar to those in-line units. Also, the original oil cap "handle' was a solid bridge across the top where some later replacement GM ones have two "ears". Somewhere in the mid-80s, they changed the headlight switch printing where the originals showed the side of a headlight to a round bulb.
Luckily I've been able to score the original-looking valve and a couple of original style oil caps and headlamp switches. There's probably other stuff too, but I can't think of any at the moment. Brake master cylinder nuts (and everywhere else that nut was used) changed too. Original Nylocs had green nylon inserts, but the replacements are simply crimp nuts. GM parts fit and function as the original part, but they never guarantee they will look the same. I think the sway bar nuts are the same part number, but I can't recall at the moment.
Oh, one more thing, if anyone has purchased Olds V8 oil dipsticks in the past several years, GM did not change the number, but started putting yellow T-handles on them. Imagine my surprise finding that out. Usually when a part changes vendors or design, it gets a new part number. But apparently not always. So be on the lookout for that kind of thing.