By the way, I checked various chronologies and only thing I found was that Imphal was bombed by 34 Japanese planes on 16 May 1942 according to the World War II Chronology compiled by US military (
https://www.fold3.com/image/286800619). Same source just say on 10 May that Imphal was bombed, and has nothing on 18 May for the raid on Silchar.
I also checked 5 Sqn ORB, the only fighter RAF unit then in Assam, but it has no entries between 5 May (moving to Dinjan) and 16 June 1942. Don' know what happens to ORB between these dates, or if someone bothered to write it at all, but from 16 June Form 540 is fairly detailed (compensing the fact that there is no Form 541 before February 1943).
Last I am reading the book "First Burma Campaign", by E CV Foucar. Interesting book, but so far nothing on the raids on Assam. On 10 May 1942 a fierce battle took place on the Chindwin River at Shwegyin, which was bombed by Japanese aircraft on 7 and 9 May. By the way, the author apparently uses only Allied sources to estimate Japanese losses both on the ground and in the air, so overestimated them a lot.