Mellone lists the "unknown" cachet as #2 (Thermographed). The C. Stephen Anderson cachet as #17. Both are considered relatively common cachets from that period.
The Scott Catalog lists all of the National Defense Covers (1c, 2c & 3c) at a value of $7.00 per cover. On the secondary market, 25% of that value is more likely to be the resale value, suggesting that they may be worth possibly $1.75 to $2.00 at best. The sloppier handwriting (as opposed to typewritten addresses) could likely diminish that value even further.
In fact, a good monitor of the value of these covers is what is listed on
ebay. Right now several of these covers are for sale at a BIN price ranging from $3 to $8, and NO BIDS on any of them, suggesting that they are either overpriced or way too common to garner much interest among collectors.