Longlife III vs Top Tec 4200 vs Longlife 3

Dear Madam/ Sir,

I am writing to inquire regarding the difference between the various kind of oils available for my car.

Being a Liqui Moly customer for over 10 years, I have been servicing my most recent car (Skoda Fabia II 5J,1.6 16V (2007 - 2010)) with Longlife 3 5w30 for the last 4 years.
Since I strive to always use the same oil for my oil changes, I ran occasionally into the situation that Longlife 3 was out of stock and did not know if other Liqui Moly alternatives are the same oil, but a different packaging/ labelling or they are indeed a different recipe.

Example:
I currently use:
- Longlife III 5W-30  Art.-Nr.: 20647
Alternatives that I have found:
- Top Tec 4200 5W-30 New Generation  Art.-Nr.: 3707
- 5W-30 Longlife 3 Art.Nr: 20616

The other reason for asking is related to mixing the oils. I am currently driving roughly 30.000 km/ year, meaning that I change the oil every 6 months and with a capacity of 3,6L oil at every oil interval, I am bound to have spare oil from a 5L canister. Because the oil is kept in a dark cool place and is being used within 6 months, I prefer to use up the entire leftover from the 5L and open a new bottle to finish the oil change.
Are the above mentioned oils mixable?

Thank you in advance for your time and support.

Thank you for the answering the 2nd question regarding the recommendation about mixing.

What about the similarities or differences between the 3 types in the idea that when I am performing the oil change, it is impossible to completely deplete the used oil from the engine block.
What I am afraid of is that the additives from one oil type might react with the additives from another oil type and harm the engine, bit by bit (foam, clot or something else, I don't know)