Hi LucasPlantHub,
Your
Aglaonemas (Aglaonema) are really pretty!
Is it possible to ask the nursery grower, or the person you acquired your plants from whether or not they are named cultivars? Some nurseries mass produce plants without giving them cultivar names and I don't know of a national or international Aglaonema registry, so I guess growers can propagate plants and place whatever name they choose on them. If a plant is not labeled at the time of purchase, it might be impossible to know for certain that it has a name, other than the genus name Aglaonema.
Your plants in
photos #1 and #2 look identical to me but I've never heard of Aglaonema 'Red Cochin' or 'Boxer' but perhaps they are just not sold here in the U.S.A. where I live. You can scroll through photos here in our database:
https://garden.org/plants/sear... where you may find plants with similar leaf shape and color variegation but again, I'm not sure how you can know for certain if your plants were not labeled at the time of purchase:
Your plant in photo #3 resembles two Aglaonema I found in our database:
Chinese Evergreen (Aglaonema 'Mystic Fire Topaz')
Chinese Evergreen (Aglaonema 'Prestige')
Your plant in photo #4 reminds me of two that I have.
Chinese Evergreen (Aglaonema 'Osaka') I purchased my plants from two different sources, one was labeled 'Osaka' and the other 'Spring Snow'. To confuse things even more, it's also sold by some growers with the name of 'Diamond'.
The Aglaonemas were all from our house. We have many plants here. I'm just confused with Aglaonemas because they have many varieties. I just put their common name - Chinese Evergreen when I post to sell. I also looked into the database before and found "Prestige" looks like #3. Some say, #4 is a "Snow White." 
It's difficult to tell which is which. Most of them are almost same features.
Yes, when there's no way of knowing for sure of a cultivar name, all you can do is label them with something like the following:
