25. In doubt if recited after blessing:

See Chapter 3 Halacha 5!

One who is in doubt as to whether he has recited an after blessing, is not to repeat it, following the general rule by all Rabbinical blessings of Safek Brachos Lihakel. This applies even for Meiyn Gimel.[1] The one exception to this rule is regarding one who ate a satiating meal of bread, as explained there in Chapter 3 Halacha 5. In all cases of doubt, if one has more food available, then he should simply eat a Kezayis of more food [with repeating the before blessing even if it is the same food as he had Hesech Hadas[2]] and then say the after blessing on behalf of all the previous foods.[3]

[1] See M”B 209:10; Piskeiy Teshuvos 208:17 footnote 134-138; Admur Seder 2:1 and Kuntrus Achron 168:1 who rules that Mieyn Gimel is rabbinical

If one ate to the point of satiation: The above rule applies even if one ate a Meiyn Gimel food to the point of satiation, as according to the main opinion Mieyn Gimel is rabbinical, as explained in Halacha 1 above and in Chapter 1 Halacha 1. However, according to those who rule that it is biblical then indeed the blessing would need to be repeated even in a case of doubt. [See Piskeiy Teshuvos ibid footnote 136]

[2] P”M Pesicha 2; Birchas Habayis 1:3

[3] M”B ibid