MPS/MPL began in 1971; the Mesa name was adopted in June 1974; an Alto cross-compiler worked in spring 1975. Cedar is both a language (an extension of Mesa, e.g. by a GC, but the OO features proposed by Lampson were never implemented to my knowledge) and a development environment. I assume your claim is about the latter. The programming language doesn't have anything in common with Smalltalk, and the fundamental work even predated the latter.