Yes that is indeed the case.
route-map test permit 20
match ip address prefix-list route-filter
set as-path prepend 65100
ip prefix-list route-filter seq 10 deny 18.104.22.168/28
ip prefix-list route-filter seq 15 deny 22.214.171.124/29
ip prefix-list route-filter seq 20 deny 126.96.36.199/27
In the route-map lines 20 - it is set to "match ip address prefix-list route-filter"
Since the deny is in place in the prefix list, take it as "Not these ones"
Everything else is permitted and AS-Path prepended.
After line 20 there is no other - ACL logic - explicit deny - so if there is no match, its a deny, so the prefix's in the prefix-list "route-filter" are not advertised.
This line 20 seems to be the "catch all" other routes except for these ones i.e. that prefix list, and prepend them.
Check the routes you are advertising them as I stated in my first post with "show ip bgp neigh x.x.x.x advertised-routes" which should correlate with the route-map applied to your BGP peer.
Hope this makes it clear.