^The figure in question is the vertical lines, an important factor in determining overall sharpness and scanline thickness. Right or wrong, that does say 600 lines.
https://en.wikipedia.org/wiki/Television_lines
None of the pics you posted prove anything. The XM29 looks different from a PVM because it has a shadow mask (not aperture grille) and I'm betting NEC did not use the same SMPTE-C phosphors as Sony did with its pro monitors. From what I've seen, the XM29 looks so different from a Sony that direct TVL and scanline comparisons can't be drawn.
Compare these XM29 pictures:
http://www.bluegamer.net/wp-content/uploads/2014/10/IMG_20141021_091749.jpg
http://2.bp.blogspot.com/-AgxB9BwiJ1s/Vb1UnumddUI/AAAAAAAAC0o/vRbzYQTCZIg/s1600/480i.png
To these PVM-2950Q pics:
http://i.imgur.com/LTKFXz7.jpg
http://i.imgur.com/Ubt5hPV.jpg
Look at the difference. It's like using megapixels to decide between two completely different types of cameras!
Anyway, I was doing a bit of Googling and was led back to an old thread here regarding large 15Khz monitors.
http://www.neo-geo.com/forums/showthread.php?19783-RGB-Monitor-List
"Here's a list of RGB 15khz compatible monitors I found on Usenet you guys could use for projects.
Here's a list of some older 15KHz monitor specs."
Size Make Model MaxRes HScan DP VRef
42 Mitsubishi AM-4201R 1280x1024 15.7-64 Khz 1.1 45-120 Hz
42 Mitsubishi MegaView Pro 42 (AM-4201R) 1280x1024 60 Hz 15.75; 20-64 Khz .96 45-120 Hz
37 Mitsubishi MegaView 37 (XC-3716C) 1280x1024 75 Hz 15-39.5 Khz .85 40-120 Hz
37 Mitsubishi MegaView 37 Plus (XC3717C) 1024x768 75Hz 15-61 Khz .85 40-120 Hz
37 Mitsubishi MegaView Pro 37 (XC-725C) 1280x1024 75 Hz 15.75; 24-64 Khz .85 40-120 Hz
37 Mitsubishi Diamond Scan 37 800x600 15-36 Khz 1.1 40-120 Hz
37 NEC MultiSync XP37 (XP3778A) 1280x1024 1524-78 Khz .85 40-120 Hz
37 NEC Multisync XM37 (XM3750A) 1024x768 1524-61 Khz .85 40-120 Hz
35 Mitsubishi AM-3501R 640x480 15-35 Khz 1.0 40-75 Hz
33 Mitsubishi MegaView 33 (XC-3315C) 800x600 60 Hz 15-38 Khz .83 40-120 Hz
33 Mitsubishi Diamond Scan 33 1024x768 15-38 Khz .83 40-120 Hz
29 Mitsubishi MegaView Pro 29 (XC-2930C) 1280x1024 75 Hz 15-82 Khz .79 40-120 Hz
29 Mitsubishi Diamond Pro 29 1280x1024 15-82 Khz .79 40-120 Hz
29 Mitsubishi MegaView 29 (AM-2725A) 640x480 66 Hz 15-39 Khz .76 45-100 Hz
29 NEC MultiSync XM29 (XM2950) 1024x768 15-50 Khz .75 40-100 Hz
29 ViewSonic ViewSonic 29 GA 1280x1024 60 Hz 15-64 Khz .75 45-160 Hz
28 Aydin Controls Spectrum Autosync 9026 800x600 15-38 Khz .74 50-90 Hz
27 Mitsubishi AM-2752A 640x480 15-39 Khz .76 45-100 Hz
27 Mitsubishi AM-2752 640x480 15-39 Khz .76 45-100 Hz
27 NEC MultiSync 4PG 1024x768 15-50 Khz 40-120 Hz
27 Sony PVM-2530/BS 640x200 15.734 Khz .73 59.9 Hz
26 Mitsubishi Diamond Pro 26M (HC3505SK) 800x600 15-38 Khz .31 45-90 Hz
24 Image Systems M24LV-65MAX 1280x1024 15-80 Khz NA 55-90 Hz
21 Image Systems C21LV-65MAX 1280x1024 15-80 Khz .29 55-90 Hz
21 Image Systems M21LMUMAX 2048x1536 15-65; 48-108 Khz NA 55-90 Hz
21 Image Systems M21LV-65MAX 1280x1024 15-80 Khz NA 55-90 Hz
21 Sony PVM-2030/BS 640x200 15.734 Khz .55 59.9 Hz
20 Aydin Controls Spectrum Autosync 9008 1024x768 15-38 Khz .28 40-90 Hz
20 Mitsubishi Diamond Scan 20LF 800x600 15-38 Khz .31 45-90 Hz
20 Mitsubishi Diamond Scan 20LP (HC3925L9ATK) 800x600 15-38 Khz .31 45-90 Hz
20 Mitsubishi Diamond Scan 20M (HC3925ATK) 800x600 15-38 Khz .31 45-90 Hz
20 Sony GVM-2020 800x600 60 Hz 15-36 Khz .55 50-100 Hz
20 Taxan Supervision 970 640x48060Hz 15-37 KHz .31 50-90 Hz
19 Barco CD-351 1024x768 15.5-23.5 Khz .32 50-60; 72-80 Hz
19 Conrac 7250 1280x1024 15.73-37 Khz .31 Hz
19 Microvitec 1019 800x600 15-36 Khz 40-100 Hz
17 Image Systems M17L-T 1600x1280 15-65/48-108 Khz NA 55-90 Hz
15 Electrohome C15 Series 15 1024x768 15-50 Khz .28 45-90 Hz
15 IDEK / Iiyama MF-5015 800x600 15.5-37 Khz 50-90 Hz
15 IDEK / Iiyama MF-5015A 800x600 60 Hz 15.5-38.5 Khz .31 50-90 Hz
15 Princeton Graphics Multiview II 640x870 15-70 Khz NA 75 Hz
14 AOC CM314 800x600 15-35 Khz .31 50-80 Hz
14 Commodore 1950 (AOC CM314) Up to 800x600 15-35 Khz .31 50-80 Hz
14 Darius TSM-1431 800x600 15.75-39 Khz 50-90 Hz
14 IDEK / Iiyama MF-5014 800x600 15.5-37 Khz 50-90 Hz
14 Magnavox CM1352 640x200 15.7 Khz .42 47-62 Hz
14 Mitsubishi Diamond Scan 14 (AUM-1381A) 800x600 60 Hz 15.6-36 Khz .31 45-90 Hz
14 Mitsubishi FA-3415 800x600 15.7-35.5 Khz .28 45-80 Hz
14 Nanao FlexScan 8060S 640x480 15-35 Khz Hz
14 Nanao FlexScan 9060S 800x600 15.5-38.5 Khz .28 50-90 Hz
14 NEC MultiSync II 800x600 56 Hz 15.5-35 Khz .31 50-80 Hz
14 Panasonic PanaSync C-1391 1024x768 (i) 15.5-36 Khz .31 40-80 Hz
14 Princeton Graphics 1400 (Utra 1400)~A Multisync 15-36.5 Khz 45-120 Hz
14 Relisys RE-5155 800x600 15.5-35 Khz Hz
14 Sony GVM-1310 800x600 60 hz 15-36 Khz .25 50-100 Hz
14 Sony PVM-1354Q 640x200 15.734 Khz .25 59.97 Hz
14 Sony PVM-1351Q 640x200 15.734 Khz .37 59.97 Hz
14 Sony GVM-1311Q 800x600 60 Hz 15-36 Khz .25 50-100 Hz
14 Sony PVM-1390 640x200 15.734 Khz .37 59.97 Hz
14 Taxan Supervision 770+LR 640x48060Hz 15-35 KHz .31 50-90 Hz
14 Taxan Supervision 770+ 640x48060Hz 15-35 KHz .31 50-90 Hz
14 Taxan Supervision 775 640x48060Hz 15-38 KHz .28 50-90 Hz
14 Wen JM143E 800x600 15.75/30-37 Khz .68 48-90 Hz
13 Aydin Controls SP 1499 1280x1024 15-40 Khz .31 40-90 Hz
13 NEC Multisync 3DS 800x600 56 Hz 15.8-38 Khz .28 50-90 Hz
13 Sony CPD-1303 800x600 15.75-35.5 Khz .37 50-100 Hz
13 Sony CPD-1402E 640x480 60 Hz 15-34 Khz .25 50-100 Hz
13 Sony CPD-1302 800x600 60 Hz 15-34 Khz .25 50-100 Hz
13 Sony CPD-1302A 800x600 60 Hz 15-36 Khz .25 50-100 Hz
10 Sony CPD-9000 640x240 15.75 Khz