Reverse Lookup not working

[Seguin, Ronald]

I don't understand why one of the reverse lookups failed and the other 
succeeded based upon the in-addr.arpa files defined???????

nslookup 206.47.229.167
Server:  pluto.in.bellnexxia.net
Address:  205.207.237.48

*** pluto.in.bellnexxia.net can't find 206.47.229.167: Non-existent
host/domain


nslookup 206.108.105.62
Server:  pluto.in.bellnexxia.net
Address:  205.207.237.48

Name:    sms2-quebec14-fe7-0.in.bellnexxia.net
Address:  206.108.105.62


more 229.47.206.in-addr.arpa

21              IN PTR  sms1-hamilton14.in.bellnexxia.net.
38              IN PTR  sms1-windsor12.in.bellnexxia.net.
54              IN PTR  sms1-sudbury98.in.bellnexxia.net.
74              IN PTR  sms1-london14.in.bellnexxia.net.
183             IN PTR  sms2-london14.in.bellnexxia.net.
92              IN PTR  sms1-kitchener06.in.bellnexxia.net.
102             IN PTR  sms1-kingston08.in.bellnexxia.net.
156             IN PTR  sms1-quebec14.in.bellnexxia.net.
167             IN PTR  sms2-quebec14.in.bellnexxia.net.

more 105.108.206.in-addr.arpa

38              IN PTR  sms5-montreal02-fe7-0.in.bellnexxia.net.
42              IN PTR  sms5-montreal02-fe7-1.in.bellnexxia.net.
54              IN PTR  sms6-montreal02-fe7-0.in.bellnexxia.net.
58              IN PTR  sms6-montreal02-fe7-1.in.bellnexxia.net.
73              IN PTR  sms7-montreal02-fe7-0.in.bellnexxia.net.
81              IN PTR  sms7-montreal02-fe7-1.in.bellnexxia.net.
78              IN PTR  sms8-montreal02-fe7-0.in.bellnexxia.net.
85              IN PTR  sms8-montreal02-fe7-1.in.bellnexxia.net.
62              IN PTR  sms2-quebec14-fe7-0.in.bellnexxia.net.
66              IN PTR  sms2-quebec14-fe7-1.in.bellnexxia.net.