See the Ramban to Vayikra 7:38. There he says that the commandments the Jews received the (almost complete) year they spent camped in the Sinai Desert after the giving of the Torah (Bamidbar 10:11) are referred to as being given at Mount Sinai, because they camped in its vicinity.
The Lubavitcher Rebbe, in Likkutei Sichot volume 27, page 279 (link in Yiddish), learns that Rashi (Vayikra 25:1) understands it the same way (that laws were given throughout the year the Jews camped in the Sinai desert).
When Rashi says:
ובא הכתוב ולמד כאן על כל דבור שנדבר למשה שמסיני היו כולם כללותיהן ודקדוקיהן, וחזרו ונשנו בערבות מואב
Scripture states this [phrase] here to teach us that [just as in the case of Shemittah,] every statement [i.e., every commandment] that was conveyed to Moses came from Sinai, [including] their general principles and finer details [and that the commandments delineated in Deuteronomy were merely] repeated and reviewed on the plains of Moab [not originally given there].
His use of "from Sinai" instead of "from Mount Sinai" were exact, since it includes the Torah taught during the year they spent at Sinai.