The mess on the tape after a recording, especially if you were recording over something else or trying to "insert", is the result of your VCR not having something called a "flying erase head". VCRs erase before they record, and the erase head is normally some distance away from the record head, so when you stop recording there's a varying amount of tape after that that's erased, garbled or mostly erased. With a "flying erase head" the erase head is part of the main drum and only what is being recorded over is erased.

These were present mostly on high-end and/or editing models. Since VCRs are all but dead, I'm not sure that any current models actually have that feature.