Gosh, Terence, if I knew that I needed to make a purchase, I'd not be posing a question here. I did already make a purchase, though it may not have been the correct one.
Before you read on, by all means, let me know what I need to purchase. I say that because the rest of my post is partly a rant, though a reasoned one.
So I've worked this issue both backwards and forwards. I bought the latest version of iPhoto, version 9.4.1. But when I booted it, i was told that I needed version 9.x.x. The older version kept asking for the next oldest version. OK. So I went the other way. I started with my own version: 8.1.2. I added updates 'til I arrived at this impasse: both the 8 series needed the very first 9 series and the oldest 9 series needed the very first 9 series. That version, acc to Apple, is called version 9.0.1. It doesn't exist on Apple's update/upload pages. I used Google to find a discussion of it. Great! Not only did I find a discussion, the writer was kind enough to hotlink "9.0.1" to the web page on which it, supposedly, was available. No such luck: Both times I tried, I got the same Apple page which did not offer 9.0.1, but only 9.1.
The goal: use iPhoto and Preview to edit my RAW files. I have downloaded the (free) latest update to do so. Now all I have to do is to get iPhoto (and Preview) to work.
If, when starting from 8.1.2, a purchase was needed, it sure would have been great had Apple made a note of it. If there was no way to get from 8.x.x to 9.x.x without a purchase, it sure would have been great had Apple made a note of it somewhere.
I pointed out that you needed to purchase as you made no mention of having done so. But gosh Timothy, pity I have an aversion to sarcasm, so I'll limit my contribution to this:
1. If you bought 9.4.1 on the App Store there is no need to update anything
2. If the 9.4.1 update you bought on the App Store doesn't work, contact App Store support.