Well, I tried the standard search field (relevanssi) but for some reason it doesn't work on this page. It does on other pages ...
So I thought I'd go about it in another way ...
Attaching images to be more clear on what happens when I try to use the normal search field.
(the field is added to Relevanssi and I rebuilt the index)
Apart from the images, this is the url that the search generates: hidden link
&dt=1534694400
&wpv_aux_current_post_id=6808
&wpv_aux_parent_post_id=4249
&wpv_view_count=6803-TCPID6808CPID4249
&wpv_post_search=A%3A06
Addition to my last reply, I notised that it doesn't work as it should on other pages either.
Searching for A:05 returns A:03
(A:05 does exist).
See image.