after 1.5 upgrade and mods, getting several PHP Notice messages

I don't know what all has been done on this site though I did do the 1.5 upgrade. What seems to be happening is that instead of bypassing the original files in languages and reading only the files in the override folders, it is reading both and therefore throwing errors for every definition:
[17-May-2012 06:28:20] PHP Notice: Constant TEXT_PRODUCT_NOT_FOUND already defined in /home/kustom/public_html/kooziez/includes/languages/english/product_info.php on line 10

In other places, it's ignoring if statements as in the case of the ultimate seo where it says if (defined('FILENAME_NEWS_RSS')) $seo_pages[] = FILENAME_NEWS_RSS; then the error reads:

[17-May-2012 06:28:20] PHP Notice: Use of undefined constant FILENAME_NEWS_RSS - assumed 'FILENAME_NEWS_RSS' in /home/kustom/public_html/kooziez/includes/classes/seo.url.php on line 192

I have found evidence that mods were added partially in places before I got into this so I would say it's an easy guess that the upgrade did not cause these problems. Any ideas what has gone wrong?