So if those are big tabs, what do the lil tabs look like?
Prior to 1975, the bowl vents had a single small tab identical to the tab on your limes lid vent. The tab on the lid vent was changed to large by 1978.
I'm borrowing some photos for visual aids here.
Credit goes to Zorknards2 & Jeff for the first two photos. I hope its ok to use these.
Here's an example of the "squared" small tabs. From zorknards2 1956 black kettle. This style would go until the early 60s.
Here's an example of the bowl vents after the early 1960s, but before 1975. This is from Jeff's Patent Pending avocado 22.5.
Around 1975, Weber retooled the bowl vents to the large dual tab style. This is from my 1978 brown kettle.