I was wondering if someone knows the answer. I send my films to a film lab to be developed, I got back the pics and checked the negatives. 6 of the pictures weren't printed, though they are still visible and clear to see on the negatives what's on them. Most of them were clearly not fully good, like I accidentally opened the back and half of a photo got destroyed, or others are quite underexposed. I don't know much about film labs so that's why I wanted to ask: Why were they not printed? Did the film lab made the decision in my place judging them as bad and undesired photos? "Bad" photos are still very useful to me as I like to experiment here and there and if I don't get the end result it's harder to say what I messed up. (I'm asking here and not the lab because I don't directly go to them, I send the film through someone else and only in about once a month.) Thanks in advance for any answers!
This answer is pure speculation:
The reason probably is because of automatic system for print which check if the photo is with good exposure and only then print it on paper.
And maybe you should ask the lab these questions.
As recommendation: let the lab develop the film then you scan it, edit it and print (at home or via other service). Also you can try to ask lab (as suggested from @Tetsujin) to print everything (if they can).
"checked the negative, around 6 photos were not developed."
If it was roll film, and they were on the negative, then they were developed. They might not have been printed. But printing is a different process that happens after the negatives are developed and uses the developed negatives (though, just to head off drive by comments, there are edge cases that fall under "alternative processes").
Generally due to the much smaller market for film lab services today versus in the last century, fully trustworthy film labs are the exception rather than the rule. In part this is due to the way complex automated development equipment has aged (most of it is old). In part this is due to the lower volume making it economically difficult to hire expertise in production positions. In part it is due to the aging of highly experienced technicians who gained expertise in high volume operations in the previous century.
What this means is that you won't just have to go through a trial and error process with your camera. You can also expect to go through a trial and error process to find a film lab capable of reliable development.
I recall in the 1980s having to either tick a box marked "PRINT ALL" or handwrite that on the stub, at the time of submitting the film for processing.
When the packet of photos came back, there were several outright failures, but I got a completely white or black sheet of developed photo paper for each one. At my cost of course.
Back in the days before digital cameras, I did a little amateur astronomical and scientific photography and then had to get the photos developed. These photos would sometimes be mostly black, and to a casual observer it probably seemed like they were taken with the lens cap on. If they were on the same roll with some shots of my kid's birthday party, the results would come back at the supermarket with just the birthday shots printed. I think this was just a case where an actual human was involved, and they were trying to be nice and save me money. I tried writing on the envelope "PLEASE DEVELOP ALL SHOTS," but that never worked.
I worked in a photo developing and printing lab for a very well known photographic brand in the early 1990s, so this answer is based on my experiences and the processes in place then.
All film was developed and printed (unless damaged) but the roll of prints (from multiple rolls of films - maybe 70 or more 35mm films) was subject to a manual check after processing. At that point the customer advice labels were applied and any apparently “junk” photos were struck through once or twice with a chinagraph pencil. Any prints with a single strike were just binned by the print cutting machine. Double strikes meant those prints were filtered out and put to one side to have that frame more “manually” (though note that it wasn’t fully manually) reprinted.
Any requests for “please print all” would be handled in a separate batch such that the prints were not marked for disposal when checked - though likely at the risk of not being returned to the customer quite as quickly, as “standard” batches of films for processing and printing at 6” x 4” were prioritised for overnight return to the customer.