According to the CambridgeGEL, headquarters has the same singular and plural form, but HQs is the plural of the abbreviation of "headquarters".
Aren't both statements contradictory? Apparently people use it as fallows:
A company with one headquarters has an HQ. A company with two headquarters has two HQs. According to Wiktionary, hdqrs (plural hdqrs).
Yet, does h.q. or H.Q. have a similar plural?