大方廣佛華嚴經隨疏演義鈔 77.6

77.6

疏「安籌雖是後事」等者，恐人設難云：既是毱多建窟，乃是佛滅之後百年中事。今是始成說經，那是彼窟？故為此通。

Regarding the Commentary's statement 'Although the placing of counting-sticks was a later event' and so forth: this is for fear that someone might raise an objection saying: Since it was Upagupta who built the cave, it was a matter occurring within the hundred years after the Buddha's extinction. Now, this is the time when the Buddha first attained [enlightenment] and preached the sūtra; how could it be that cave? Therefore, this explanation resolves it.