In a BuJo: list the page you want to reference. I also create several pages of initial index at the beginning of my BuJo, and generally put spreads at the back, working forward.

That way the BuJo reads as: index, calendrical pages, spreads/references (at the end).

The advantages are non-electronic storage with ready reference. You can only access the current year's BuJo generally (unless you're where your archive is kept), but current references should be readily available on you (e.g., addresses, current information, calendar, etc.). You can only lose the current journal should you misplace it, and the information won't leak out readily as it can from digital storage.

For an index-card system, look up Zettelkasten if you haven't already. Very robust and useful indexing systems have been at the heart of academic and commercial research for over two centuries now, and the systems developed are quite powerful. Digital systems are more powerful still, but have their own downsides: loss or corruption, data exfiltration, and devices which may not be convenient to use in all circumstances.

With a BuJo or Zettelkasten, information capture is possible by carrying a few index cards with you and jotting notes. You have capture, can file these into your journal (or an indexing system, or a loose-leaf binding), and don't risk losing the rest of your archive in the process. The lack of digital distractions is its own powerful benefit.