I believe they got a Title 1 warrant for Carter Page. I was disappointed that Nunes didn't fight harder when the 702 renewal came up, but maybe in some closed session he saw that it would be futile, and anyway they probably would (and probably did) spy on Trump without a warrant.
Yep, 5o USC 1800, et seq, and in my opinion, the 1804/1805 warrant was sought to obtain 1809(b) insurance policy, immunity from criminal prosecution for warrantless snooping. In other words, snooping didn't start with the warrant, and the point of the warrant wasn't to "authorize snooping." The FBI and other agencies snoop when they feel like it, for any purpose, and the law is a toothless hag.
Sundance did a very good job of laying out speculation on the relationship between the blanket warrantless surveillance described in 702 surveillance, 5o USC 1881, et seq, and the specific court orders directed against Carter Page - the subject of the dueling HPSCI memos. Read Tying All The Loose Threads Together - DOJ, FBI, DoS, White House: "Operation Latitude".
"Unmasking" of the names or ID or US persons can happen in the context of both searching the foreign communications database that is obtained without a warrant (702), and the communications obtained under a Title I court order. Both protocols include "minimization" procedures, which is essentially "masking" procedures.
What Admiral Rogers found unjustified unmasking (violation of agreed minimization) in the 702 database. Whatever minimization tightening followed from his detection would not transfer to a Title I search program.
The country has been down this road before. Somehow the fact of wholesale government snooping on the public becomes a point of discussion. Some outrage is ginned up to comfort the public, hearings are held (for example, the 1973 Church Committee), laws are passed that are promised to "fix this so it never happens again," and the ultimate effect of the law is to legalize an expansion of the wholesale snooping on the public. The FISA law didn't rein in snooping, it expanded it, and even created a "star chamber secret court" to make it appear the snooping had third party oversight to protect privacy interests. We have no more privacy against our government than the North Koreans have against theirs. Same, same. We just waste more money on a facade that calls itself "privacy protection."