Here are the collocates of AGO computed using the written section of the BNC, ordered by frequency.
There are nearly 17,000 instances of AGO, and YEARS is the top collocate, found 9,000 times near AGO. The "Relation" column is blank and at this point it is only possible to sort each column by its frequency or to sort the words alphabetically. What's needed is a way of knowing how closely each of these collocates of AGO is related to it. Are A, THE, WAS etc. really closely linked to AGO?
If we now choose Compute | Mutual Information in the menu,
and select a suitable wordlist to use for the comparison:
then we get the following list when sorted by clicking the Relation column:
The top items in the list now reflect much better the tendency of AGO to accompany periods of time and numbers. [The top collocate (HENSLEY) only occurs 5 times with AGO (out of 17 altogether in the whole BNC Written).]