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You could reveg, try take two clones of one plant and grow them in different conditions to really check what the issue could be. My two cents, its probably just strain dependent. I'm only on my second grow, and my bud density qualms from the first grow were resolved by changing strain Everything else stayed the same.

You see the spacing is tight with the auto which is grown outdoor with the sun. Where your indoor plants have large internodal spacing. This gives me reason to believe its a light issue. You mentioned you using a 8 year old blurple light. I would recommend getting a new light such as a LED quantum board. I have a 120w quantum board from Green Houston, next to my old 100w Mars Hydro 48 reflector in one tent. (70cm x 70cm) and they work great together. When looking for a quantum board always look for ones with Samsung diodes. Ill provide the link to the one I purchased. There are different sizes and versions. But any quantum board that uses Samsung diodes such as LM301H diodes will be excellent. https://www.greenhouston.co.za/products/quantum-board-led-125w Depending on the size of your tent you might have to go larger or buy multiple. However if you just get one Quantum board, you can combine it with your old light.