If my precinct was not to report in within a reasonable time after poll closing, I would be expected to call in with the reason. This actually happened once because someone was not there to lock up the polling place.
Within minutes, they gave me the OK to bring everything in and leave the place unlocked. Were I not to show up with my precinct results, they would send the constable to arrest me.
The other poll workers are to sign off the results on the readout tape and post them in the front window of our polling location to prevent these type of shennagins. When 100% of precincts are reported in, no other ballots other than the provisional and absentees (as deemed eligible) are to be counted. At least, that's the way things work in a Pennsylvania country bordering the county (Allegheny) with our 2nd largest city (Pittsburgh).
Where I work election day in NJ, many years now, there are always party reps who see the print outs when machine is closed and call results in to HQ. Can even take photos. Each results copy is signed by the 4 board workers.
All results are brought to city hall along with all voting materials
That was my experience in Fairfax County, VA as Chief Election Officer for a precinct. Upon opening the polls, we validated and recorded the metal numbered seals as well as verified that the machines read 0 and the protected counters showed what our documentation said they should.
Closing the polls was very similar. We tabulated the results, including write-ins, and sealed up all machines, recording the numbers of the security bands used.
The final results were written out and posted on the door of the polling place when the facility was closed. The tapes, provisional ballots, and memory cartridges were returned to the County election office that evening.
It’s not difficult to have safeguards against shenanigans, but good processes which are time-tested need to be put in place and you need people who are dedicated to tight security.