You've basically claimed that Beyonce has sold 250-400m albums in the past 10-12 years in a time when she's released 3 albums. This would put her up there with the Beatles and Elvis in terms of albums sales overall and could be even more than MJ sold in his entire career with just those three albums! This is an eyebrow raising claim - to say the least. Naturally I assumed that there would be journalists etc documenting this incredible success and how it isn't reported in the official figures but I can't find a single article anywhere or any source even claiming such incredible sales.
Wikipedia lists official certified album sales and 'claimed' album sales. Many artists have much higher claimed sales than officially certified sales as you suggest. Beyonce is only about +20m for claimed sales though. She may well be humble but if there's a credible claim to those sales I'm pretty sure it would have made it on Wikipedia by now.
Regarding the relatively low sales of Lemonade. The album only streamed on the Tidal platform for a number of years which will have killed her numbers in the age of streaming. This makes me even more sceptical of the overall claim because she severely restricted the market for the album for the entire time it was hot. I don't think its that surprising that an artist sells so many copies in the first week either, as keen fans are desperate to get the new release. The songs on that album didn't do well in the singles chart, relative to her previous work. The numbers are not that impressive on Wikipedia and it's worth noting that a platinum single would only qualify as 150000 album sales if gained through streaming.
Like I said it's not a claim - this isn't too uncommon within the music industry because RIAA certifications are only as valuable as the money it costs to get them updated - especially for some of the bigger artists who came up pre-streaming era, there's just too many certifications to update & it's very expensive once piled up.
In comparison with artists who came up in the last 10 years or so who get their certifications updated yearly because platforms like Spotify & Twitter encourage the competition that it fuels and it's cheaper to do it that way. It's just marketing at the end of the day, and a lot of the biggest artists don't need the apparent 'value' or bragging rights it brings.
Journalists aren't talking about it because it's not new, and Beyonce isn't the only one this applies to. She is an extreme example, but that's mainly because she's gone out of her way to close off information about her (side note: she also hasn't informed Forbes of her Net Worth in almost the same amount of time) and every Beyonce fan knows this about her, so it's not newsworthy. The only people not aware of this are those who aren't her fans, and I doubt they care either.
I guess you can go here:
https://www.riaa.com/gold-platinum/?tab_active=default-award&se=beyonce#search_section
and sort by date - you'll see most of them were last certified around the same time of release, or a few years after release - and the majority haven't been updated in over 10 years.
Like I said in my initial point, Crazy In Love (released in 2003) sold 500k units in 2019 alone. But has only certified 500k sales total in the US all time, on the RIAA website the last certification was in 2006 - we're talking about one of the biggest records in the last 20 years, to think it's only sold & streamed 500k worth of units in the US is madness.
Likewise with songs like Halo, Single Ladies & Irreplaceable which not only dominated the charts but are intwined in pop culture too - Halo for example has 900 million streams on Spotify alone, according to RIAA though - in the US it's only sold 2 million units ever - both physical & streamed. Single Ladies came in 2008 sold 4 million units in less than 2 years, and hasn't been certified since 2010 - I mean come on, that's ridiculous!
You don't have to believe me of course, but some maths would definitely let you know that things aren't adding up.
Funnily enough you bringing up Lemonade made me remember that despite it only being available on Tidal for about 3 years and only coming on Spotify in the last 2/3 years it has 2 songs which have racked up over 250 million streams on Spotify alone - those same songs, according to RIAA have only sold 1 million each. The album itself sold about 600k it's first week and remained on the charts for a considerable amount of time, because the Tidal exclusivity meant that more people were pushed to buy the album - on RIAA though it went 2x Platinum in May 2019 then 3x Platinum in June 2019 - I also believe this coincides around the time it became available on Spotify - which tells me that as soon as it became available on the platform the popularity surged immensely, and it hasn't been updated since.
I've hand picked a few songs but hopefully you can see just how complex this whole situation is, especially once you start adding in stuff like streaming because I believe things like youtube views, credits in media like movies/tv shows etc all count towards streams in recent years (I could be wrong) and since 90% of her RIAA hasn't been updated since 2010, we've barely scratched the surface of the amount of sales from streams.