Our Telepresence units did not have the "External Manager" field configured even though they had static IP addresses. I assume in the past, these devices may have originally been setup for DHCP and had somehow cached CUCM/TFTP details.
Based on the Telepresence device admin guides, I concluded that the "External Manager" field should be configured as no Option 150 would be provided by DHCP.
An update on Step 3.
I accidentally installed cmterm-s52010ce8_2_1.k3.cop.sgn on the CUCM publisher, instead of the device pack. Without a reboot, I noticed the Device Default had "s52010ce8_2_1.pkg" in the Cisco Telepresence MX200 G2, MX300 G2 and SX20 fields.
So that answered the question on what the phone load name is.
After installing the device pack on the CUCM publisher and rebooting, I looked in the TFTP File Management for any other files starting with "s5". There was only the one above.
Based on this, I concluded that the Cisco Telepresence firmware files are not included in the CUCM device pack . I could be wrong?
I installed the SX10 firmware file (s52030ce8_2_1.pkg) and the CUCM Publisher.
52030ce8_2_1.pkg showed up in device default in the Cisco Telepresence SX10 field
I installed all 3 cop files (MX300 G2, SX10 and Device Pack) on all remaining nodes.
And rebooted each node and waited for all services to start, individually starting with the publisher.
I believe this reboot process reset the Telepresence devices and therefore kicked off the upgrade a little prematurely. The upgrade did not take very long, and all devices upgraded successfully.