Just remembered a couple of things, with bottling we didn't tighten the lid fully until they came out of the pressure cooker, then as they cooled the seal was made by the higher pressure outside pushing the glass down onto the rubber seal. Then you always checked before storage and before use that the seal was good. Tin cans are completely sealed before going through the cooker and the contents are at atmospheric pressure. Originally tin cans were done in the same way as glass bottles, these days, a small vent was left in the lid then after cooking while still hot this was sealed with solder..