I am using Ubuntu mate too, and in my system there are 75% packages are supported until 5 years.
this is screenshot of my Ubuntu mate 16.04 LTS
now running the command you can see that packages related to desktop environment are supported for 3 years and those system related are supported for 5 years.
now in this screenshot you can see that these packages are supported for 3 years and they are mostly related to mate desktop environment like caja,mate panel,mate-desktop-environment-core..etc
As Ubuntu flavors are based on some other desktop environment like lubuntu is based on LXDE,these desktop environments are not in control of canonical which had made Ubuntu.but unity which is default desktop environment of the Ubuntu is made by canonical and thus they are in full control of the unity desktop environment,thus they provide 5 years of support to maximum packages.
The best information I have been able to find about the program is this. It seems to spell out in detail the level of service as well as the response times you can expect for varying levels of severity. Certified hardware is of course better supported.
Hopefully someone with personal experience can provide you with a better answer.
Best Answer
Run command
source https://www.ubuntu.com/info/release-end-of-life
I am using Ubuntu mate too, and in my system there are 75% packages are supported until 5 years. this is screenshot of my Ubuntu mate 16.04 LTS
now running the command you can see that packages related to desktop environment are supported for 3 years and those system related are supported for 5 years.
now in this screenshot you can see that these packages are supported for 3 years and they are mostly related to mate desktop environment like caja,mate panel,mate-desktop-environment-core..etc
As Ubuntu flavors are based on some other desktop environment like lubuntu is based on LXDE,these desktop environments are not in control of canonical which had made Ubuntu.but unity which is default desktop environment of the Ubuntu is made by canonical and thus they are in full control of the unity desktop environment,thus they provide 5 years of support to maximum packages.