Increase from Tango to Tango Plus
 

Just tried to make a booking YVR-YYZ.
Usually the difference between Tango and Tango Plus is about $ 30.00 on this route. Checked for middle of September, there are a lot of flights at $ 199.00 in Tango but all Tango Plus fares are $ 142.00 more = $ 341.00.
Is that going to be common from now on or is it just not adjusted yet, seems like fares came down in Tango and maybe Tango Plus just hasn't been adjusted yet. Does anybody have similar experience on different routes?

More information on the route and dates would help, but remember that there are several sub-sets of fares in both TANGO and TANGO PLUS, so on the days you are looking at, the lowest TANGO PLUS fares may be sold out, while the lowest TANGO fares might still be available, thus giving you the highest difference in costs on that route between fare categories. BTW What is the lowest LATITUDE fare showing?

One afternoon when I was playing arround I tried five or six "domestic" city pairs and found that the Tango-TangoPlus differential was $30 accross the board, whether it was a Rapidair flight or a transcon.

I checked all the dates for the whole week of September 16th - September 24th. There were quite a few flights available at $ 199.00 Tango fare but to go to Tango Plus as mentioned on all fares was $ 342.00 on a couple of them the difference is even bigger, $ 199.00 to $372.00. It's very unusual.
Latitude is at its usual around $ 641.00.
You are probably right that the Tango Plus fares are all sold out but Tango fares are still available as demand for fares where you can get status miles is much higher. Just never experienced such a big difference all across the board of low Tango fares. I wouldn't be surprised if the Tango Plus fares would come down in the next few days.

Take the Tango and Run -and maybe get an MCO!
 

FWIW I found that the difference is constantly changing. If it means a lot to you, consider waiting or just consider the Tango fare is a bargain and go for it. If you choose not to pay the fee for the advance seat selection, you might still be able to do it on web check in. If it is oversold, you will be subject to an involuntary bump if you have no assignment, giving you an MCO and full AP miles on the J class on the next flight.