Approx 2 weeks ago, I updated the phone (via settings app) to /e/OS v 1.11 (e-1.11-s-20230511288805-dev-berlin).
Ever since that, the trust center on the phone shows the vendor image as outdated: “vendor image: a few months old”. System information shows vendor is from 11-2022.
Why are these images not updated by the /e/ updater and can I safely flash the new versions (by executing both fastboot commands again but with the newer images) without:
There are already (old) topics on this community but sadly, the question has never been answered definitively.
Since this is also my first post here, I want to use this chance to thank everyone from the e.foundation team for providing such a great alternative to the spyware android from google. I love you all <3
I have the same reporting on my Asus Zenfone 8, where it also says that the vendor image is outdated. However, it was a bit of stunt getting the /e/ installation working for this model, where with an older version of the vendor image only side loading was kicked off ultimately.
I’ve checked on a Friend’s Fairphone 4 with /e/ on that was installed with the easy installer. There it correct and updates the vendor image properly, was reporting up2date.
The question also is: Is it problematic in terms of security, when the vendor image does not get updated with the regular /e/ OTA updates?
is certainly an issue that is less than ideal. I would very much like to see this resolved. The /e/OS build does containdtbo.img + vendor_boot.img but at install time the components are required “out of sequence”. Users can produce their own dtbo.img + vendor_boot.img from the /e/OS build using this method OnePlus - 9 Pro - lemonadep - Documentation Suggestions - #8 by bofh666.
Secondly, is berlin, as a 2021 device, still receiving manufacturer firmware revisions ? November 2022, does seem a rather short period of support. 
You also see the date of the last manufacturer firmware revision represented as Vendor security patch level here.
Settings > About phone > Android version > Vendor security patch level
There will have been as you say
multiple new updates to these images. the newest one is from 2023-05-20
… but we do not know if there actually is any manufacturer firmware revision included, or available to include.
Once a Google property, the Lenovo-owned manufacturer has fallen from grace in the software department. It’ll generally stick with two OS updates and two years of security patches for flagship, and possibly one OS bump for other devices.