On Thu, 20 Feb 2020, Steve Willner wrote:
This is a version of "Eddington bias," and it would have been my
first thought to explain the effect too. ...
Bias questions are difficult, and I'm not sure the effect isn't an
observational bias, but it's not obvious to me it is.

Well, the paper didn't include the following 55 SDSS quasars which
have brightened from the POSS-I epoch (1960-ish) to the SDSS epoch
(2005-ish) . This is a very partial list, I have over a thousand of
these. So I'm seeing data bias in the paper. Eric

Rmag SDSS SDSS POSS POSS
(Cousins) 2005 2005 1960 1960
# name change rmag gmag rmag omag
-- ------------------------ ----- ----- ----- ----- -----
1 PKS 1222+21 -2.17 16.10 15.88 18.21 18.36
2 SDSS J101340.06+104116.0 -2.11 18.49 18.80 20.45 21.07
3 SDSS J002021.19+180708.3 -2.03 18.33 18.58 20.22 20.46
4 SWIREJ160947.05+550533.3 -1.98 18.42 18.16 20.35 20.53
5 SDSS J133904.14+161831.6 -1.96 18.81 19.13 20.61 21.08
6 SDSS J020406.98-052842.8 -1.93 18.26 18.38 20.07 20.62
7 SDSS J163210.13+440705.9 -1.87 18.72 18.61 20.51 20.74
8 SDSS J101337.31+613234.9 -1.81 18.31 18.49 19.99 21.00
9 SDSS J131706.97+473358.0 -1.80 18.17 18.01 19.90 19.97
10 SDSS J013447.29+212907.5 -1.79 18.94 19.17 20.59 21.08
11 SDSS J212246.17-011314.6 -1.77 18.66 18.74 20.32 20.38
12 2QZ J140000.7+015827 -1.73 18.48 18.52 20.11 20.55
13 SDSS J084542.82+151642.0 -1.71 18.70 18.70 20.31 20.72
14 SDSS J105210.02+165543.7 -1.69 16.41 16.63 17.96 18.40
15 SDSS J135520.97+385058.2 -1.68 17.64 17.71 19.21 19.81
16 SDSS J154439.17+354819.1 -1.68 18.84 19.22 20.35 21.20
17 SDSS J023602.76-051526.9 -1.68 18.92 19.02 20.48 20.77
18 7C 0912+2532 -1.68 17.77 17.89 19.33 19.57
19 SDSS J024001.70-054559.3 -1.67 18.39 18.28 19.98 20.24
20 SDSS J152108.00+144438.1 -1.66 18.70 18.78 20.25 21.74
21 SDSS J024302.64-021546.0 -1.65 19.32 19.47 20.85 21.30
22 SDSS J154612.90+385349.8 -1.64 18.88 18.95 20.41 21.12
23 SDSS J120933.13+401246.6 -1.64 18.84 19.03 20.35 20.83
24 FBQS J0130-1019 -1.63 17.83 18.02 19.33 20.04
25 SDSS J174251.80+542949.2 -1.63 18.83 19.12 20.31 20.62
26 SDSS J022101.06-072628.9 -1.62 18.50 18.65 20.00 20.24
27 TEX 1147+022 -1.61 18.59 18.67 20.09 21.38
28 SDSS J115506.79+123326.2 -1.59 18.68 18.87 20.14 21.82
29 4C 12.35 -1.59 18.04 18.24 19.50 20.78
30 SDSS J141819.79+212910.3 -1.59 18.69 18.77 20.17 20.93
31 SDSS J162919.58+190530.3 -1.59 18.86 19.13 20.30 20.36
32 PKS 1502+106 -1.59 18.22 18.53 19.66 19.75
33 SDSS J134031.02+570129.6 -1.58 18.54 18.65 20.00 21.29
34 SDSS J012108.88+224558.6 -1.58 18.79 18.82 20.27 21.08
35 SDSS J103111.30+043211.4 -1.57 18.42 18.44 19.89 20.36
36 SDSS J131437.74+042644.0 -1.56 18.42 18.52 19.86 20.56
37 SDSS J144249.81+053228.8 -1.56 19.26 19.26 20.72 21.12
38 F864:072 -1.55 18.83 18.91 20.27 21.30
39 SDSS J072952.43+441146.0 -1.55 18.54 18.56 19.99 20.35
40 SDSS J025420.59-073745.5 -1.55 18.62 18.76 20.05 20.31
41 SDSS J085538.58+235005.4 -1.55 18.73 18.96 20.14 20.50
42 SDSS J155829.23+530704.1 -1.54 18.91 18.85 20.36 21.44
43 2QZ J125309.5+012830 -1.54 18.23 18.46 19.63 20.46
44 SDSS J162329.86+255531.7 -1.53 18.88 19.11 20.27 21.37
45 SDSS J094915.33-005921.3 -1.53 18.93 18.99 20.35 20.84
46 SDSS J023439.04+010740.1 -1.52 18.77 19.06 20.14 21.77
47 SDSS J113111.14+373709.1 -1.52 18.20 17.98 19.66 20.29
48 SDSS J023805.37-001652.1 -1.52 18.49 19.08 19.80 21.45
49 SDSS J080132.80+073413.5 -1.52 18.58 18.82 19.96 20.79
50 SDSS J120849.25+303332.9 -1.52 18.05 17.95 19.49 19.62
51 SDSS J095617.02+022901.7 -1.52 19.36 19.66 20.73 21.14
52 SDSS J084422.46+351034.9 -1.51 17.90 17.83 19.33 19.69
53 SDSS J133808.74+304113.7 -1.51 18.96 19.00 20.37 20.46
54 SDSS J233402.44+061302.4 -1.51 18.64 18.63 20.05 20.09
55 2QZ J142343.2+014306 -1.50 18.33 18.54 19.69 20.53