I pickled zucchini slices last summer with plenty of vinegar, sugar and spices and still have some jars in my refrigerator. They look fine but I wonder about bacteria etc. Thanks
It is impossible to answer this. Normally, food is quite clearly divided into the categories of "perishable" and "shelf stable", with perishable food being safe for 3-5 days in the refrigerator and shelf stable food being safe indefinitely prior to opening.
Refrigerator pickles are one of the very rare cases in the middle. They are not shelf stable (else they would be suitable for canning), but they are still not very pathogen friendly. Just how much slower is bacterial growth in them? It will differ from recipe to recipe. And just saying "plenty of vinegar" is not at all sufficient to predict a real use-by date. Not even the exact recipe in gram of each ingredient would be sufficient for this, since bacterial growth is a complex system, which makes it practically impossible to calculate such a prediction.
Your only information source is your original recipe. If it gives you a time period, you should use that (and hope it is trustworthy). If it doesn't, then there is no way for somebody to just say how long it is safe.