What year did Browning change from the front safety to the cross-bolt safety on the classic A5 shotgun?

1952 was the first year that FN made Brownings with the cross bolt safety as standard. I have seen a few guns made in 51 with the cross bolt and I have seen at least one 1952 gun with a front trigger safety. Many of the older guns were converted by Browning to switch the front trigger safety to crossbolt. You can tell this if there is a slot in the front of the trigger guard. If the customer paid, he could have a new trigger guard installed along with the conversion, thus it is not possible to date a gun by the safety alone. FN continued the front trigger on their guns that they sold worldwide until the early 60's. These were not Browning Arms Co. guns