F1 or maybe not?

Why do some varieties get called F1 on some seed suppliers but no F1 mention on others?  Can I check anywhere please?

I grew Rosella tomatoes this year from Premier and they are lush.  Performed well, taste gorgeous, thin skin but not as prone to splitting as black cherry or black opal. I am saving seeds to share on here, but need to clarify if they are F1 or not. 

https://www.premierseedsdirect.com/produ...y-rosella/


https://www.seedaholic.com/tomato-f1-rosella.html

Any advice please? This tomatoes really impressed me, so I would love to share them.