So how did you find out about this kind of stuff prior to internet making information searchable?
Let's imagine I was sent back to 1970, in a time-machine, with no money, or anything, except basic clothing. Let's also assume I can keep my knowledge of electronics and stuff, but have to forget any specific datasheets I may remember or pin-outs.
A library of that era (or borrow from friends/clubs/educational-establishments), would probably/potentially have electronics books and magazines, for reference. One can then take notes (for free), on paper. E.g. The TTL 7400's Pin out.
You can do odd-jobs, or pocket-money or something, and get some £cash.
From various places, shops and/or mail-order, you can get, perhaps priced in shillings. Grab bags of miscellaneous, transistors, diodes, resistors, capacitors, integrated circuits, logic ICs, etc.
If you are handy with an analogue meter, you can identify the lead connections on a transistor (resistance mode of meter, there are techniques for doing it, fairly quickly), measure its Hfe, and estimate its capabilities, from the size of its package (power/current handling of transistors/diodes, power rating of resistors, capacitors often have their capabilities, printed on them).
Logic ICs, can be hand datasheet'ed. I.e. Let's say it is the era of TTL logic, which 1970 mostly was (there was still other types such as DTL, RTL etc). The power was usually 5V+ on the highest number pin, and ground for the diagonally opposing pin e.g. Pin 7 GND and pin 14 +5V, on a 14 pin DIL.
By probing (multi-meter or logic-probe or even just a resistor plus LED (bit early for them, to be widely available), or small filament lamp, buffered by a transistor.
Then you can try out the connections, as the outputs will be somewhat obvious, the rest are inputs (ignoring power connections), and assume it is either AND/OR/NAND/NOR/XOR/INVERTERS, as an initial guess. It is a bit like tying your tie. I could fairly easily do it, but describing how to do it, would be a real pain. You just go through and experiment for a few minutes, and somewhat rapidly, decide what it is.
More complicated logic, such as decoders/flip-flops, would be much harder to determine.
Suppliers, especially in later decades, would be happy (sometimes free, sometimes perhaps 10 pence or more, per sheet, photocopies of the applicable datasheets).
Also, there were books, with lots of transistor specifications in them (usually big tables), from a wide range of manufacturers. Typically called something like, transistor substitution guides. (Towers?, was a popular one).
In the old
days, there were lots of shops, selling electronic items (components), or sold many items, but included a section with electronic items (transistors/resistors etc). It was quite possible that the shop-keeper, or one of their assistants, or even (at the right time), a knowledgeable customer. Might be able to help with your electronics questions.
Some (quite a few) items, such as TVs, Radios, etc. Actually had the schematic, inside the case. Some items instructions came with a schematic. Some components when bought, actually included a paper leaflet, with datasheet like details, printed on it. Especially (needed to request a free datasheet with purchase) Radio-spares (now known as RS), Maplins (who were happy to give free datasheets on request, if I remember correctly, also their earlier catalogs, had a lot of datasheet pin out and other information in it). Tandy (also known as radio shack, in some other countries), also typically/sometimes had datasheets, inside the IC packet.
Some of the better electronics kits (e.g. Heathkit), would come with decent schematics, and component details (pictures/outlines rather than datasheets as such).
EDIT: In later years (before the internet), if you were important enough (i.e. suitable businesses, not individual hobbyists), you could get the distributors/suppliers/manufacturers, to fax through their datasheets. Or post you the databooks, if significant enough of a customer, for them to justify doing that.
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