Reverse DNS RFCs and Recommendations

Wed Oct 30 21:33:38 UTC 2013

So in the four examples below, 3 of them preface the IP with an alpha character. Charter however, starts the rDNS off with a number. I'm not arguing with anyone but what potential problems could that cause with DNS? 
I'm also thinking of the famous  www.1and1.com, where the number "1" starts off one of the sections. 

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3. Start each section of the name with a letter, not a number or hyphen.

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> Actual Examples:
> cpe-67-XX-XX-XX.stny.res.rr.com - 67.XX.XX.XX 
> d28-XX-XX-XX.dim.wideopenwest.com - 28.XX.XX.XX 
> c-68-XX-XX-XX.hsd1.mi.comcast.net - 68.XX.XX.XX 
> 24-XX-XX-XX.static.bycy.mi.charter.com - 24.XX.XX.XX