I don't know about 'hundreds of hours', but a simple reverse look-up, which should take a matter of seconds can take a few minutes to do 'the hard way'. I know because I've just done one.
Over the years, when prices were a lot cheaper, I'd bought a number of two-tone 7A38's simply to break up for parts. I'd recently decided that I was going to re-build one - a two-tone 7A38-7280. I had most of the parts, including a decent case and bracelet, with minimal plating wear, but was missing the silver Tachymeter dial ring. Going through a stack of little boxes, I found not one but two.
Usually I'm very methodical about stocking spare parts (new or used) in little ziplock bags with a post-it note stating the Seiko part number (and where it had come from). I'd obviously overlooked these and couldn't remember exactly what they came out of. I had an idea, but wasn't sure that they were the correct shade of silver. So I went through the individual parts lists for all the 7A38's that I could remember using a silver Tachymeter ring (some of which I'd broken up for parts). According to Seiko Oceania's database, this part, which I've since determined is # 84311024 is common to:
7A38-7020 SAA010J, 7A38-7240 SAA108J, 7A38-724A SAA086J, 7A38-7260 SAA098J and what I wanted it for - 7A38-7280 SAA120J.
Incidentally, it should also be found in the parts list for 7A38-728B SAA136J (the UEFA EURO 88 limited edition), but Seiko's database erroneously shows 8431102
5. P/n 84311024 should also come up in the parts list for the two-tone 7A38-7190 SAA054J - except that model's data is completely missing. However, it does show that the stainless 7A38-7190 SAA053J uses a different (lighter silver) Tachymeter dial ring, p/n 8431102
6. The two-tone 7A38-727A SAA132J also uses a silver Tachymeter ring, which Seiko's database shows uses a different part number: 84320847. Which, I'm certain these two I've found aren't, because I've never broken one of those up.
So after breakfast, I'm going to nail it back together.