How to identify a specific page in a large file

I'm currently transcribing a large (1800+ pages) file documenting an early 20th century court martial, “Court Martial of Grover Cleveland Bergdoll.” (The accused was quite a character: wealthy draft-dodger, deserter, early aviator, race-car driver, etc. He claimed to have buried $150,000 in gold in Western Maryland. I'm still waiting to see if he recovered it, or if that was fake news!)

In a few instances I've added comments that cross-reference other pages in the file. How should I reference those other pages, which have two or three numbers. For example, see The URL includes 214, which is the number of the thumbnail in the column on the right side of the screen; it's also used in the widget below the transcription box. Is that called the "page number?" The "Download" button links to the image file, which ends in a four-digit number, in this case 1660. Maybe that's the "image number?"

Also, in this particular file, there are one or more long documents with their own page number scheme, such as the court reporter's transcript of the court martial hearing. It would be confusing if the court number typed at the bottom of the court transcript (438) was also called "page number."

My question is: what is the recommended way to refer to another page/image in the file, and what do you call these various identifiers.

Apologies for a long, geeky query. And thanks!