How many spot checks are done on the voting system? Where I live we have electronic balloting with a paper copy of the votes stored in each booth. Does the Board of Elections ever take those paper records and check that they match the precinct count? Even the threat of that makes hijinks further down the path more difficult.
How about fingerprints?
Yes, you’ve described a big weakness in the overall system. There is no system in place to comprehensively cross check all totals at every level. Hence, there are multiple entry points for fraud to be injected.
The takeaway from this is that the old ways of busing around voters and illegals to stuff ballot boxes, all the physical means of pulling off an election steal, all those ways are antiquated in the face of electronic fraud.