I did some research a few years ago, and below is what I discovered back at the end of 2014; I will perhaps update for 2015 - 2018 when I get the time!
'The (Monaco) track was resurfaced just prior to the 2010 meet there: -
http://www.presse.gouv.mc/304/wwwnew.nsf/1909$/4141C64660AF4F5EC1257727002AD7E4GB?OpenDocument&1GB
This is an interesting exert: -
"The work will focus on the resurfacing of the areas concerned: the first few centimetres of the upper layer of the track will be scraped off, then replaced by rubber resin, cast in one jointless block. This is made possible due to the physico-chemical compatibility between the new and old resin. The track will be faster and therefore conducive to new records, including at the next Herculis athletics meeting - Diamond League on Thursday 22nd July 2010."
The Monaco meet was ranked No.2 in 2009 (probably behind Zurich), but was already an established meet, with Baala running 3:30.96 in 2009.
But the fast times en masse didn't start until.... 2010!
That year the 5 fastest men all set those times in Monaco. I did a bit of research and I've put their time in Monaco followed by their non Monaco season's best time:
1. Kiprop ~ 3:29.27 (3:30.61) difference - 1.34
2. Laalou ~ 3:29.53 (3:32.75) " - 3.22
3. Choge ~ 3:30.22 (3:31.81) ' - 1.59
4. Wheating ~ 3:30.90 (3:37.52! - although he ran a Mile in 3:51.74 which = 3:34.57, so I'll take that) - 3.67
5. Gregson ~ 3:31.06 (3:35.42) difference - 4.36.
That's an average difference of 2.84 secs faster at Monaco for those athletes. The fastest non Monaco performance in 2010 was Kiplagat's 3:30.61 in Berlin.
2011 was a bit of a down year, but the meet still produced 4 times in the top 10 for the year.
2. (second fastest that year) Kiplagat ~ 3:30.47 (3:31.39) difference - 0.92
6. Chepseba ~ 3:31.74 (3:30.94) difference + 0.80 * The only athlete in the past 6 seasons (5 if not counting this season) listed here that has run a faster time on another track other than Monaco .
7. Kaki ~ 3:31.76 (didn't run any other listed 1500 that year)
8. Willis ~ 3:31.79 (3:33.22) difference - 1.43
15. Cheboi ~ 3:32.45 (3:33.82) " - 1.37
That's an average of 0.73 secs faster at Monaco for the 4 with other listed times for 1500 that year. The fastest non Monaco performance in 2011 was Kiprop's 3:30.46 in Rieti.
2012 had 6 athletes in the top 10 coming from Monaco's race: -
1. Kiprop ~ 3:28.88 (3:29.78) difference - 0.90
3. Chepseba ~ 3:29.77 ( 3:29.90) " - 0.13
5. Willis ~ 3:30.35 (3:34.70) " - 4.35
6. Makhloufi ~ 3:30.80 (3:32.58) " - 1.78
7. Birgen ~ 3:31.00 (3:31.17) " - 0.17
9. Kiplagat Seuri! ~ 3:31.61 (3:33.27) " - 1.66.
That's an average of 1.50 secs faster at Monaco for the 6 with other listed times for 1500 that year. The fastest non Monaco performance in 2012 was Kiplagat's 3:29.63 in Doha.
2013:-
1. Kiprop ~ 3:27.72 (3:31.13) difference - 3.41
2. Farah ~ 3:28.81 (no other listed 1500 for 2013)
3. Ndiku ~ 3:29.50 (3:33.41) difference - 3.91
5. Birgen ~ 3:30.77 (3:31.90) " - 1.13
6. Tanui-Ozbilen ~ 3:31.30 (3:35.09) " - 3.79
7. Cheboi ~ 3:31.53 (3:32.85) " - 1.32
That's an average of 2.71 secs faster at Monaco for the 5 with other listed times for 1500 that year. The fastest non Monaco performance in 2013 was Kiplagat's 3:30.13 in Rieti.
2014:-
1. Kiplagat ~ 3:27.64 (3:29.70) difference - 2.06
2. Kiprop ~ 3:28.45 (3:29.18) " - 0.73
3. Kwemoi ~ 3:28.81 (3:31.48) " - 2.67
4. Souleiman ~ 3:29.58 (3:30.16) " - 0.58
5. Iguider ~ 3:29.83 (3:32.09) " - 2.26
=6. Wote ~ 3:29.91 (3:30.86) " - 0.95
=6. Willis ~ 3:29.91 (3:34.72) " - 4.81
10. Manzano ~ 3:30.98 (3:34.40) " - 3.42
11. Centrowitz ~ 3:31.09 (3:32.70) " - 1.61
That's an average of 2.12 secs faster at Monaco for the 9 with other listed times for 1500 that year. The fastest non Monaco performance in 2014 was Kiprop's 3:29.18 in Doha.
Monaco clearly has great credentials for fast time and is clearly the fastest/best track in the world for middle distances. This analysis doesn't prove it is in any way illegal, and is certainly not short, but it does raise the question as to why top athletes run on average of 2.03 secs faster (based on the data of the 29 athletes above over the 5 seasons, 2010-2014) on the Monaco track than on any other, over the course of the season?
I would suggest looking at the above data that the number of 'fast times' increased by 2012 and thereafter, as athletes realised that it was an incredibly fast track.