All three are "on the property", but only one is done with the mod to the new UA configuration.

The second one went into mod on 3/24/19 and the third one went in on 5/1/19. All three will be in the new Low Density configuration of:

46 Bus/First
22 Premium Econ
47 Econ plus
52 Econ

As far as original UA aircraft go, there are still 7 older 767-300s (92-93 builds) that show as not slated for either Polaris or the Low density config. There are 10 767-300s (98-01 builds) that show they are planned to get Polaris Low Density plus 4 more that are already converted. There are 14 767-300s (91-93 builds) that already have been converted to the regular density Polaris config. The regular Polaris config and the old 2 class config have the same number of seats (30 and 184) so, those two configurations can be easily interchanged during the time when aircraft are going through the Mod.

So, as we see older aircraft get the Polaris mod (14 91-93 builds thus far) that is at least some indication that they are planning to keep the older builds a bit longer. Hopefully we will see the 7 remaining older 767-300s get Polaris, giving further hope for keeping those aircraft a little longer.