Last month I was working on transferring the audio from an audio cassette to digital. The audio was the recording of a conversation of my great grandfather and a historian at the local university. The cassette that I was working with turned out to be a copy of a copy from the original. From what I can guess the copies were made not with a dual-tape deck but with a microphone and two separate decks. This leads to increased noise and low signal, making some parts of the cassette difficult to understand. What I've learned from converting countless analog sources is that the best results for digital transfer will always come from the analog original.
Copying analog to analog is like making a photocopy (just Xerox it!). The imperfections on the page add up over time and after a few copies the image quality of the photocopy has decreased significantly. Alternatively, digital copies are the same every time. This is because to be digital is, at the most basic form of the media, a series of "0"s and "1"s.
For those who haven't heard this explanation before, let me break it down for you. The screen that you are reading this blog on displays light through pixels. The more pixels in the screen, the higher the resolution. For example, the latest iPhone screen has a pixel resolution dimensions of 1125 (width) x 2436 (height). This comes out to 2,740,500 pixels in the handheld device! Each one of those pixels is simply a box that can display a separate light value, color, or brightness. What decides the pixel output is the information provided by the input source, such as color and brightness. When each pixel does its job correctly, the screen displays the image or text that the program provided information for. This means that changing from analog to digital is to create a representation of the original with a definitive value for each pixel in the resulting digital image.
To put it in the context of NorCal Film Co., if you are try to convert a VHS tape that is a copy from an 8mm film the quality will be worse than if you converted the 8mm straight to digital. In summary, make sure your memories are captured at the highest possible quality by converting from the originals.