Tosefta for Terumot 4:12

[If there are] five collections [of produce] on the threshing floor, terumah [may be] taken from one on behalf of all, said Rabbi Yehudah. When is this? At the time that the major part (עיקר) of the [produce of the] threshing floor still remains. If the major part of the threshing floor does not remain, terumah is taken from each collection separately. One who brings produce inside his house, even though they are scattered (מְפוּזָּרִין, see Megillah 13b:18), he [may] take terumah from one on behalf of everything. [If there were] two piles that were heaped together (see Ter. 4:12), he takes terumah from each and every one. If had sacks of produce or rounds of fig cake or דוגיות of dried figs, we [may] take terumah from everything in one basket, and take tithes from one on behalf of the other.

He had before him two boxes [of terumah], one of wheat and one of barley, and one of them fell [into a larger container of chullin] and one of them got lost, and it is not known which one fell and which one got lost, both of them are permitted.