Since DL no longer has a published award chart showing required mileage amounts for each cabin for each region, it's become more difficult. But through some searching, you can still find some baseline values to go off of. For example, current "Low" for TATL Business Class to Europe from the US is 140K miles round trip (last summer it was 125K r/t). Thus if you find a TATL J ticket for 140K miles r/t, you've found one for "Low". If DL is running mileage sales, you may even get lucky and find some below the "Low" inventory (last summer tickets were as low as 105K or so). If DL is charging is charging more than 140K r/t (say you found an itinerary for 200K miles r/t), then this is not the "Low".

One way to tell what the low is (at least for international travel) is looking for partner awards. For example, if you find a TPAC on Korean Air to ICN for 80K one way (160K r/t), this is "Low", as partner awards will always require what is the current "Low" rate (again, even though this won't be published), though there are also variations to this rule even. I haven't looked in a while but there was a point where to Australia, it was 95K one-way for J on partner Virgin Australia, while DL "Low" for LAX-SYD was requiring 110K one-way.

More specifically to Mr. Tickets' post - what he means by "there is no guarantee that they will load lowest award space at the same time" is that when DL loads the flight 331 days out, they may not elect to load it at their lowest inventory level. For example, DL rarely releases "Low" to SYD from LAX, even 331 days out. If you can find it, snag it (I got lucky and snagged 2 "Low" J tickets on partner VA to BNE from LAX for this past February, booked in April of last year). While "Low" in J on DL metal to SYD from the US is 110K in J now, it's not uncommon for DL to release the inventory charging 175K to 225K or more (I've seen as high as 400K one-way in J on the DL metal flight to SYD). But that doesn't mean that that flight won't come down from 350K to 225K or from 225K to 175K or 110K. It's all what DL's revenue management department decides.

Best advice is to have flexibility, play around with it, and if you see what you think is a good deal, book it. If you have questions about a specific amount for a specific route, you can always ask here for feedback (though of course, waiting for responses carries the risk of that inventory disappearing before you book and with this being FT, you may get varying opinions on whether it's a "good deal"). This is why one of the biggest benefits of Platinum and Diamond Medallion status - award redeposit fee waiver. We can book one flight and if something better opens up (better date or cheaper option), cancel and rebook without penalty.