.htaccess - Conflicting rules in htaccess prevents 404 page from bring displayed -

i have condition check non-existing page , display 404 page accordingly. however, rule doesn't works when i'm in sub-directory 'cms' due conflicting rule. how can fix this? code shown below:

#this worked fine   rewriteengine on rewritecond %{request_filename} !-d  rewritecond %{request_filename} !-f  rewriterule ^ /404.html [l,nc]  #with rule 404 not show #e.g. mywebsite.com/cms/non_existent.php not show 404 page rewriterule ^events/  cms/callers.php [l] rewriterule ^event/(.*)/  cms/callingparty.php?eventid=$1 [l] rewriterule ^cms/(.*)/(.*)/ cms/showpage.php?param1=$1&param2=$2 [l] rewriterule ^cms/(.*)/ cms/showpage.php?param1=$1 [l]