Certain keywords gives different time periods.

So I'm trying to extract the top tweets (most popular etc) aimed at certain companies since the beginning of 2018. This is the code I'm using in terminal:

python /Users/jamesozden/Google\ Drive/Staff\ folders/James\ Ozden/3Keel\ work/GetOldTweets/Exporter.py --querysearch "lidl plastic" --since 2018-01-01 --until 2018-07-04 --toptweets --maxtweets 20

Which gives me what I want, the top 20 tweets from the previous 7 months (attached).

However when I change "lidl" to "tesco", it only gives me the toptweets from the past week (also attached).

Any idea why this is the case? I've also been doing it through a VPN in case they blocked my IP address and no avail.