Merge of log files from old and new RPi servers is simply a concatention:

cat 202008-old.log.gz 202008-new.log.gz | gzip -d > 202008.log

gzip -d < 202008-old.log.gz | tail 
2020/08/21 17:10:51Z 26.6875 =F@26CB;X0;T11 11 W255 0 F255 0 W255 0 F255 0;S 14 20 c;C5
2020/08/21 17:22:51Z 26.625 =F@26CA;X0;T11 23 W255 0 F255 0 W255 0 F255 0;S 14 20 c;C5
2020/08/21 17:58:51Z 26.6875 =F@26CB;X0;T11 59 W255 0 F255 0 W255 0 F255 0;S 14 20 c;C5
2020/08/21 18:06:51Z 26.625 =F@26CA;X0;T12 7 W255 0 F255 0 W255 0 F255 0;S 14 20 c;C5
2020/08/21 18:26:51Z 26.5625 =F@26C9;X0;T12 27 W255 0 F255 0 W255 0 F255 0;S 14 20 c;C5
2020/08/21 18:46:51Z 26.5 =F@26C8;X0;T12 47 W255 0 F255 0 W255 0 F255 0;S 14 20 c;C5
2020/08/21 19:10:51Z 26.4375 =F@26C7;X0;T13 11 W255 0 F255 0 W255 0 F255 0;S 14 20 c;C5
2020/08/21 19:38:51Z 26.375 =F@26C6;X0;T13 39 W255 0 F255 0 W255 0 F255 0;S 14 20 c;C5
2020/08/21 19:58:51Z 26.4375 =F@26C7;X0;T13 59 W255 0 F255 0 W255 0 F255 0;S 14 20 c;C5
2020/08/21 20:06:51Z 26.5 =F@26C8;X0;T14 7 W255 0 F255 0 W255 0 F255 0;S 14 20 c;C5
% gzip -d < 202008-new.log.gz | head 
2020/08/21 21:12:49Z 26.5625 =F@26C9;X0;T15 17 W255 0 F255 0 W255 0 F255 0;S 14 20 c;C5
2020/08/21 21:24:49Z 26.5625 =F@26C9;X0;T15 29 W255 0 F255 0 W255 0 F255 0;S 14 20 c;C5
2020/08/21 21:28:49Z 26.5 =F@26C8;X0;T15 33 W255 0 F255 0 W255 0 F255 0;S 14 20 c;C5
2020/08/21 22:00:50Z 26.4375 =F@26C7;X0;T16 5 W255 0 F255 0 W255 0 F255 0;S 14 20 c;C5
2020/08/21 22:08:50Z 26.375 =F@26C6;X0;T16 13 W255 0 F255 0 W255 0 F255 0;S 14 20 c;C5
2020/08/21 23:08:50Z 26.375 =F@26C6;X0;T17 13 W255 0 F255 0 W255 0 F255 0;S 14 20 c;C5
2020/08/21 23:16:50Z 26.3125 =F@26C5;X0;T17 21 W255 0 F255 0 W255 0 F255 0;S 14 20 c;C5
2020/08/21 23:40:50Z 26.375 =F@26C6;X0;T17 45 W255 0 F255 0 W255 0 F255 0;S 14 20 c;C5
2020/08/21 23:56:50Z 26.4375 =F@26C7;X0;T18 1 W255 0 F255 0 W255 0 F255 0;S 14 20 c;C5
2020/08/22 00:00:50Z 26.4375 =F@26C7;X0;T18 5 W255 0 F255 0 W255 0 F255 0;S 14 20 c;C5