Have you tried looking up "ASP104" or "ASP104N1" in any of your databooks/catalogs? That's the marking on the die and might yield some closer clues.
Unfortunately this is the type of thing that Google is absolutely horrible for finding information about, although it wasn't that bad a decade or two ago. Asking on some electronics forums might also get some better suggestions or even an exact ID.
I doubt the "P" is for "Philips" but just indicates Pin 1.
I've tried slicing and dicing the part numbers, but couldn't come up with anything. I've found that Google is not bad; the biggest problem is IC suppliers who list basically every possible part number with no information. I think their business model is that if you want to buy the part for a high price, then they will see if they can find it somewhere.
The limit for me is the early 1980s. After that, the feature sizes get too small for my microscope. (Red light has a wavelength of 700nm, so things start to get difficult below about 1 micrometer.) And when chips have two or more layers of metal, it is much harder to follow the wiring.
Companies that do chip analysis commercially, and have tools such as electron microscopes, can process much more complex chips. The limit for them is probably how much you're willing to pay.
Christopher Tarnovsky has given a few DEF CON and BlackHat talks (eg [1]) where he describes reverse-engineering Trusted Platform Module(TPM) and smartcard chips. It's a good demo on the capabilities of the sort of thing where companies are limited only by the time they can afford to take.
