Redirect requests only if the file is not found?

# If requested resource exists as a file or directory, skip next two rules
RewriteCond %{DOCUMENT_ROOT}/$1 -f [OR]
RewriteCond %{DOCUMENT_ROOT}/$1 -d
RewriteRule (.*) - [S=2]
#
# Requested resource does not exist, do rewrite if it exists in /archive
RewriteCond %{DOCUMENT_ROOT}/archive/$1 -f [OR]
RewriteCond %{DOCUMENT_ROOT}/archive/$1 -d
RewriteRule (.*) /archive/$1 [L]
#
# Else rewrite requests for non-existent resources to /index.php
RewriteRule (.*) /index.php?q=$1 [L] 

From Rewrite if files do not exist

How about this?

# If requested resource exists as a file or directory go to it
RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule (.*) - [L]

# Else rewrite requests for non-existent resources to /index.php
RewriteRule (.*) /index.php?q=$1 [L]

I seemed to have at least one problem with each of the examples above. %{DOCUMENT_ROOT} seemed to do the wrong thing in certain places, and some / characters seem to be missing. Here is my solution, which goes in the .htaccess in the web root.

Instead of using two rules (one for the case where the file under clients/ is found, and one for not found), all I need to check is if the requested file (or directory) does NOT exist. Because if it exists, no change is needed, it can just use the file provided in the client dir. Here's the code I settled on:

RewriteEngine on
RewriteCond %{DOCUMENT_ROOT}/clients/$1/$2 !-f
RewriteCond %{DOCUMENT_ROOT}/clients/$1/$2 !-d
RewriteRule ^clients/([^/]+)/(.*)$ $2 [L]

Thanks for your help!