If I started my blog last year, why does my Stats display show pageviews from 2, or even 3, years ago?and
If I rename my blog to a better URL, how do I carry the Stats numbers to the new URL?Neither blog owner shows an accurate understanding of the historical nature of Stats pageview counts.
The Blogger servers record access activity by URL - not by blog.
Stats extracts pageview counts as needed, by URL, from the Blogger server logs. If the URL of your blog is "myfineblog.blogspot.com", and you request pageview counts for your blog, for "All time", you will see pageview counts against "myfineblog.blogspot.com", for Stats since May 2006 (as currently the case).
If the URL of your blog was "myexcellentblog.blogspot.com" until you renamed the blog to "myfineblog.blogspot.com" 6 months ago, you will see historical pageview counts for "myfineblog.blogspot.com" - which will include your blog, starting 6 months ago. You won't see pageview counts for "myexcellentblog.blogspot.com", from a year ago, because you'll be seeing historical pageview counts for "myfineblog.blogspot.com".
If someone else had a blog, published to "myfineblog.blogspot.com", before you renamed your blog to its current URL, your Stats displays could include pageview counts reflecting access to that blog. If "myfineblog.blogspot.com" was never used before you renamed your blog to that URL, it's possible that your pageview counts include attempted access to a non existent URL.
If you're using Google Webmaster Tools with your blog (and you should be doing that), you can check the access logs for "404 Not Found" events in the WMT logs. Just as a tree, falling in the forest, makes a sound even when nobody is around, so can access attempts exist against URLs where no blog is published.
Some referer spam appears to be sent to all likely URLs, ignoring whether or not a blog actually exists, at that URL. Referer spam is not unique to Blogger, and has been a problem since before Blogger became a major player in the Internet world.
If you just started a blog, or just renamed your blog to its current URL, your pageview counts can reflect historical referer spam, against your current URL, from before your blog was published to the current URL. As Blogger identifies specific referer spam campaigns, and eliminates some referer spam from Stats logs, this is one more possible cause of fluctuations in pageview counts.
If the possibility of seeing bogus pageview counts, for your blog as published to the current URL, does not please you, I will again point out that you'll get more out of your blog if you spend less time worrying about the details of the Stats displays, and more time working on your blog.
Look at activity before the blog was published as "noise", and look at current activity as "signal" - and work on improving the "signal to noise" ratio. Be aware of the value of your blog, and work on improving the value.