This can happen to even the most experienced mechanic, "Especially" on a high mileage car.
The old school manual brake pedal "down" - "up" - "down" - "up" bleed method risks over-stroking the master cylinder.

The master cylinder piston seals can get scored if they're pushed into a normally unused - corroded, region of the master cylinder's bore.
If this happens, you'll have little or no brake pedal, and will need a new master cylinder.

I strongly recommend using a pressure bleeder or put a wood block under the pedal to avoid the issue.

My most recent personal experience Over-stroking the master cylinder.
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