And the answer is
in 6.7.8 downloading custom fingerprints only shows the 1st one created.
in 6.7.9 the download shows both the custom fingerprints
So
6.7.8 gives
<DeviceFingerprint category="VoIP Phone" family="GrandStream" name="HT8xx">
<FingerprintRules>
<FingerprintRule match-conditions="ALL">
<RuleCondition name="mac_vendor" operator="contains" value="Grandstream Networks, Inc."/>
<RuleCondition name="dhcp.option55" operator="contains">
<valueList>1,2,3,6,12,15,23,28,33,42,43,51,54,66,121,125,160</valueList>
</RuleCondition>
<RuleCondition name="dhcp.option60" operator="contains">
<valueList>HT8XX dslforum.org</valueList>
</RuleCondition>
<RuleCondition name="dhcp.options" operator="contains">
<valueList>53,61,60,124,125,50,54,55,82</valueList>
</RuleCondition>
</FingerprintRule>
</FingerprintRules>
</DeviceFingerprint>
While 6.7.9 gives
<DeviceFingerprint category="VoIP Phone" family="GrandStream" name="HT8xx">
<FingerprintRules>
<FingerprintRule match-conditions="ALL">
<RuleCondition name="dhcp.option55" operator="contains">
<valueList>1,2,3,6,12,15,23,28,33,42,43,51,54,66,121,124,125</valueList>
</RuleCondition>
<RuleCondition name="dhcp.option60" operator="contains">
<valueList>HT8XX dslforum.org</valueList>
</RuleCondition>
<RuleCondition name="dhcp.options" operator="contains">
<valueList>53,61,60,124,125,50,54,55,82</valueList>
</RuleCondition>
</FingerprintRule>
<FingerprintRule match-conditions="ALL">
<RuleCondition name="mac_vendor" operator="contains" value="Grandstream Networks, Inc."/>
<RuleCondition name="dhcp.option55" operator="contains">
<valueList>1,2,3,6,12,15,23,28,33,42,43,51,54,66,121,125,160</valueList>
</RuleCondition>
<RuleCondition name="dhcp.option60" operator="contains">
<valueList>HT8XX dslforum.org</valueList>
</RuleCondition>
<RuleCondition name="dhcp.options" operator="contains">
<valueList>53,61,60,124,125,50,54,55,82</valueList>
</RuleCondition>
</FingerprintRule>
</FingerprintRules>
</DeviceFingerprint>
Sorted!
and just to confirm our Phone people plugged in more of these devices and the "just worked" . can;t be a bad thing :-)