The Gemara discusses why we cannot use last year's Se'irim or Par (that were lost before the Avodah and found after the Avodah was performed with replacement Se'irim) for next year's Yom Kipur service.
Among the answers suggested were Gezeiros that the Sa'ir would look like a Chatas she'Mesah Be'aleha, or Avrah Shenasah. When the Gemara asks why the Par cannot be used, it says that it is because of a Gezeirah that the Par may be confused with the Sa'ir. (The Gemara eventually refutes all of these answers because "Mishum Gezeirah Yamusu?!")
But the Sa'ir itself was outlawed only because of a Gezeirah. Don't we have a rule that Ein Gozrin Gezeirah l'Gezeirah? Why should we outlaw the Par because of the Sa'ir?
Q. Reese, Atlanta, GA
I did not find this Kashya in the few commentaries that I checked, though I am certain that somebody must deal with it.
Let me therefore suggest that in this case, we apply the principle 'Chada Gezeirah Hi'. This means that where the Chachamim feel that unless they reinforce the first Gezeirah with the second one, it will not hold; so they decree the two Gezeiros simultaneously, as if they were one.
Alternatively, the Gemara might indeed have answered as you suggested, only it gives two better answers, which perhaps conform more smoothly with the flow of the Sugya.
Be'Virchas Kol Tuv
Eliezer Chrysler
The end of Tosfos (DH "mi'Shoom Gezeirah Yamasu") in fact states that part of the question "mi'Shoom Gezeirah Yamasu" is in fact your point, that the Sa'ir itself was only due to a Gezeirah.
All the best,
Yaakov Montrose