Funny thing about house numbers: they have their own validation problems. For a while I lived in a building whose house number was of the form 123½ and that was an ongoing source of problems. If it just truncated the ½ that was basically fine (the house at 123 didn't have apartment numbers and the postal workers would deliver it correctly) but validating in online forms (twenty-ish years ago) was a challenge. If they ran any validation at all they'd reject the ½, but it was a crapshoot whether which of "123-1/2" or "123 1/2" would work, or sometimes neither one. The USPS's official recommendation at the time was to enter it as "123 1 2 N Streetname" which usually validated but looked so odd it was my last choice (and some validators rejected the "three numbers" format too).

I don't think I ever tried "123.5", actually.

Around here, there used to be addresses like "0100 SW Whatever Ave" that were distinct from "100 SW Whatever Ave". And we've still got various places that have, for example, "NW 21st Avenue" and "NW 21st Place" as a simple workaround for a not-entirely-regular street grid optimized for foot navigation.

123 + 0.5?