The 1947 Scott international was a 3 inch binder with double sided pages. Often the end of one country was on the front of a page and the back of that page started a new country. If one filled the album about 60 % full it was bulging. Many collectors back in the day split it into 2 binders. Also this allowed one to add additional pages for covers, varieties, etc. At some point Scott decided to start all countries on a new page and split the album into two parts 1A and 1B. Now that collectors are using mounts, this was still not good enough and Scott went with 4 parts 1A1, 1A2, 1B1 and 1B2. You now have plenty of room to add pages and spread everything out.
If you don't want to buy new albums, there are lots and lots of older Scott Internationals available through auctions, eBay
, Hipstamps, and dealers. I currently have my 1950s Volume 1 in 2 binders and am very happy with it.