Rashi doesn’t say the gematria of garti is the same as the word taryag . There
is no such word as taryag. Taryag is a combination of letters that equal 613.
Similarly when the gemara (Shabbos 55a ) says that the seal of Hakodosh Boruch
Hu is Emes.
The pshat is the seal of HKBH have these three letters Alef Mem & Sov . Not that
his seal is the word Emes. See Rashi & R. Nisim Gaon. Alef the first letter represents
Ani Rishon , Sov the last letter represents Ani Achron and Mem the middle letter
represents Ani Hu (present).
Yoma 69b The piska (note- kvital) fell from heaven and had written on it Emes.
Rashi writes” K’lomer ani maskim imachem” (I agree with you). The pshat is not
we see Hashem agreeing by sending the word Emes (true). We see it by sending
his seal of approval (alef mem sov).
Sanhedrin 64a same pshat in rashi.