Hi there!
First of all, thank you so much for your work, it’s been a pleasure to develop using your platform.
I’m writing this because I’ve been having an issue where the items in my collection are being duplicated instead of updated after uploading an excel, even though it has an special_item_row column.
Could you help me figure out why?
Hey @ouhenio, welcome to our Discourse 
Could you please share your CSV file (or at least a couple of lines of it), so we can take a look? One basic test to be done is to check if the IDs present on the column refer to your existing items IDs.
Also, do you see anything worth noting on the importer logs? You can access them at the Processes list.
BTW, thank you for posting in English! We can discuss in Spanish if you prefer (I use DeepL translator sometimes and we may even understand each other in Portuguese), but our developer team is probably more prepared to respond in English and may also be useful for new foreign users.
Hi @mateus.m.luna! I’ll stick to English for reference for future users. 
It’s very likely were not using the internal IDs of the items in the db, since we just used our own invented ids in the special_item_id column. Where can I check the internal IDs of the items in Tainacan?
Oh, that explains the issue. You can obtain Tainacan internal IDs by simply exporting your Collection to CSV.
It worked! Thank you so much for the help