I would not combine RIAA with Soundscan and here is why. U2 will most likely ship 1 million copies of the best of....1990-2000 before the album is even released on November 5. 1 million copies will have been purchased by record stores and others that sell the album to meet the upcoming demand from consumers for that album. There might not be another shippment of the album to stores for several months depending on how well the first shipment of around a million copies sells to consumers. So you can't have a weekly chart based on the shipment of albums(RIAA), because sometimes no more albums are shipped after the release date. That happened with REM's album last album that dropped off the billboard 200 after only 10 weeks on chart, yet still went GOLD(500,000) sold mainly because thats how much was shipped before the album was released. Remember, once it is shipped, as far as the artist and record company are concerned, it is an album sold. Its in the hands of the retail outlet and up to them to sell the product and make their own profit.
To sum up, shipment figures are used for total sales of an album because they are in fact just that, total sales to consumers and distributers. Soundscan represents total sales to consumers only and does not represent 100% of total sales to consumers but is very close, about 95%. An album is shipped to stores and then put on sale. Soundscan tracks the sale of this initial shipment and anymore shipments and compiles that sales info and activity on a weekly chart. More albums are shipped by the record company, as the retail outlets order more as their stocks of the album run out. But shipments happen on a irregular basis and sometimes not again if the album does not sell well. Sales to consumers tracked by Soundscan happen every day.
I agree with you though that I don't like the idea of counting each disc in the package which is what RIAA does. They do it because double albums are often worth nearly double the price of a single album sometimes and are trying to represent the success in the level of money being made from the sale of each package. A good example is Pink Floyds the WALL which has only sold 11.5 million copies in the USA, but because it is a two disc set, is certified for 23 million in sales. The WALL album cost as much as two albums and has certainly generated sales in money worth the sale of 23 million albums, But only 11.5 million "2 disc album sets" have been sold.
Still, I wish they would just count each package instead of each disc in the package. I'm more interested in the number of people that have purchased the album rather than the money made from each sale. Still, its easy enough to determine how many people have bought the album just by dividing the number of disc in the certified sales level, ex. 23 divided by 2 equals 11.5 for THE WALL.
Best Of....1980-1990/B-sides entered the chart at #2 while the single disc version entered the chart at #45. I wish soundscan would combine the two, but they won't because of the different prices and slightly different product. This is what always happens when artist release two different versions of an album at the same time.
But remember, this is a Best of........1990-2000 who's sales will be measured in years rather than weeks. Best ofs are albums of longjevity, not that initial sales burst you see with brand new product. I actually do not find the weekly sales of best of.... nearly as interesting as the sales of a brand new studio album with ALL new original material. Fact is, most U2 fans will probably not run out and buy this although the hardcore crowd will. Fact is, we already have nearly every song on this Best of....... . Best Of's, after the Die Hards like me and others buy the album, might be a good estimation of popularity among NON-fans of U2. I know that sounds a bit ironic because what exactly is the definition of a fan. This is different from a brand new Studio album like ATYCLB where every U2 fan, die hard or casual, and even "non-fans" might purchase the album. Its rather ironic that most people who will buy this "best of..." will be "die hards" or "non-fans" while most of the casual and moderate fans will not feel the need to. The only exception to this I would say would be if "Electical Storm" was a huge hit, but clearly its not a huge hit in the USA(so far) so I think its going to be the "die hards" and the "non-fans" purchasing this album mainly.