I can be krum and say pilpul. The reason the MB 107,6 of ain nedavos bshabbos is only becasue you can’t bring a korban nedava bshabbos. NOw since being mekabbel shabbos early is a private din talui in you (and lfi rov rishonim a shvus) in the Bais hamikdash they can still bring nedavos. but like i said this is krum.
But i can’t find anything else