In the western world it is rare, to miss an OSSN and excise it as pterigium without no-touch technique etc. In one retrospective study from the US it was only in 0,3% of all cases of pterygium excision.
In tropical Africa, such cases are much more often. And vice versa, it is also commom to see a very suspective pterygium, that upon pathology proves to be benign… See this: Case 1 and Case 2