Standardized isn't necessarily standard. Where I work we build a lot of military equipment. We learned the hard way than even MIL-SPEC electrical connectors will often not assemble properly if all the pieces aren't from the same manufacturer.
blame that on your MIL-SPECs or their QC system. That's the problem with anything military. It has it's own specs rather than incorporating a widely accepted standard that everybody else already uses.
I have worked at plants that supplied to the military (HUMVEE (AM General))(Bendix) and understand why nothing is as simple as it should be.
when you get out of the military realm and start dealing with the standards in civilian life, as long as quality is not the issue, there should be no problems with parts from various manufacturers. If a company has continued problems with their parts not fitting properly with those from other manufacturers, that company needs to check their quality standards. More than likely it is that particular manufacturer and not the standards they claim to be meeting.