renamed R4 proprietary codes page, need to update links

[Max Philips]

anywhere linking to the R4 .../proprietary-codes/... URLs will hit a redirect after we renamed the proprietary codes page. we should update site-internal links to avoid the redirect process

[Max Philips]

so, this was already fixed when we renamed the page. I thought we needed to do it because when adding Coverage documentation we ran into it. but it turns out we already caught it!