Regarding Moshe's response to Aharon at the end of the fifth reading of Shmini, Rashi writes that Moshe's response to Aharon (who said if we heard the leniency of eating the one time only sacrifices in mourning we shouldn't be lenient with the sacrifices of the later generations) that Moshe "wasn't embarrassed" to say "I have not heard" the law.
However, in Rashi's source, it says explicitly that Moshe "wasn't embarrassed" to say "I've heard it, but I forgot"
It would seem according to Rashi, Moshe never forgot any law, while according to the source, it says Moshe did forget
Why is there a difference between Rashi and his source?
Source: https://www.chabad.org/dailystudy/torahreading.asp?tdate=4/8/2021
20Moses heard [this], and it pleased him. כוַיִּשְׁמַ֣ע משֶׁ֔ה וַיִּיטַ֖ב בְּעֵינָֽיו: and it pleased him: [Moses] admitted [that Aaron was correct,] and was not ashamed, [for he could have covered up by] saying, “I have not heard [of this law.” Rather, Moses frankly said to Aaron, “You are right! I did hear that an אוֹנֵן must not eat from sacrifices that will be offered in future generations, but I forgot!”]. — [Torath Kohanim 10:60; Zev. 101a]
וייטב בעיניו: הודה ולא בוש לומר לא שמעתי:
{In the English here, as well as several other chumashim, they add Rashi's source of "I have heard but I forgot" after the actual words of Rashi, to try to resolve the contradiction, but it would still seem that according to Rashi's actual words, he holds differently}