Is it unusuall to find a LE with out any import markings and all matching serial numbers?
Not at all. LE's started coming into the USA in the 50's as surplus. Cost 10-12 bucks and every store in town had some.
No import mark means it came in before the 1968 NFA. The "ENGLAND" stamp found on many pre 1968 LE's is the "country of origin". Many importers/exporters stamped this before 1968.
11422 is a ROF-Maltby assigned serial number and "AT" was used in 1943.