I've never seen the term IRT and I don't understand the question. Are you asking what a "Blob Top" is or what the term IRT means? If you mean I..R.T.P. that refers to Internal Revenue Tax Paid which appears on labeled bottles during the early to mid 1900's... A great history is found online here...
In the begining when we started finding stuff, we were totally bottle term unaware. We gave some names to bottle types to identify them amongst ourselves. We called hutches 'corkers' - which was a terrrible term because there are bottles that really use corks. Anyway, we met some collectors who started using bottle lingo terminology, and we were like, "What are they talking about?" "Mineral water bottle?" "No that's a soda, I'm pretty sure". "Hutchinson bottle?" "Never heard of it but we do find these corkers . . ."