@adrian78666: the published files in Github is OSPi 1.42+ and the current version we sell is OSPi 1.43+. The difference is very minor (I believe the main difference is added PCB spark gaps at the back of the circuit board, and the components remain the same).
The resistor 3R3 is a 3.3 ohm power resistor. It replaces the fuse that was on OSPi 1.42+ because many users have started using RPi 3 which draws a significant amount of current that often triggers the PTC fuse. For that reason, the fuse is now replaced by a small resistor, which still provides the connection but will not trip if RPi starts to draw a lot of current. It’s hard to document all detailed changes partly because they are small changes that I am not sure if they are worth documenting. Also, I just simply forget to write them down.
Some of your other questions really just require some familiarity in electronics. For example, 32.768kHz crystals come in many different form factors, and they are mostly interchangeable. You can even solder through-hole components onto surface mount pads, and this is perfectly fine for prototypes. Markings on parts are often just part of the part number. For example, HC595 generally means it’s 74HC595 shift register. The marking may differ somehow depending on the manufacturer, but in general the marking is not the full part number because there is not enough space to put the entire part number. Many rectifier diodes are interchangeable. For example, D1 on OSPi is a standard rectifier with a minimum of 100V reverse voltage stand. So a lot of common diodes can fit there: S1B, S1D, M2, M7, 1N4002. We often use them interchangeable depending on what we have in stock.
Hope this makes sense.