Can old App_Web.xxxx.dlls affect site behavior?

I have ASP.NET Web Site project开发者_开发百科 that deploys as precompiled to server. After deploy bin folder contains multiple App_Web.xxx.dll files. I know that I can delete old files before deploying new version but if I don't, can these old files somehow affect web site behavior? How ASP.NET finds that my last version page had compiled to App_Web_aaaaa.dll and App_Web_bbbbb.dll contains old version?

Thanks!

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Short answer, yes it can, as you may wind up with namespace conflicts/multiple declarations that are the same. It's just safer to delete the old ones prior to deploying the new ones.