@Albert *******
the point is that the 45 day stamp is for Visa exempt entries and is not a visa. If you were simply stamped in without purchasing a visa, then you do not have a visa, and you entered via visa exempt status. If you truly had a 90 day visa, by definition, you would be stamped in for 90 days. If you were stamped in for 45 days with such a visa, then the immigration officer did not notice the visa you bought, and assumed you were coming in by visa exempt and stamped you in incorrectly for a visa exempt entry rather than using the 90 day visa you paid for.