There is fundamentally no difference between urine and blood glucose. The difference is more related to time. When you test BG, your reading is telling you what the level is now. With UG, the reading is hours old. (Urine has to collect, the bladder fill, and your cat needs to decide to use the litter box.)
Looking at Yuki's spreadsheet, it's hard to make a definite statement about bouncing. It would be very helpful if you could get a "before bed" test every night. Many cats experience lower numbers during the PM cycle. You don't want to miss any dose reduction worthy readings. It's especially important to get tests at night if you can't test during the day.You really need more data to reliably answer your question.
Could you make a note in your in your signature about which dosing method you're using -- either
Tight Regulation or SLGS? The point at which you reduce the dose and the amount of time for evaluating the dose differ between the two methods.
As to your question about bouncing, it's certainly possible for a cat to bounce, clear the bounce which may mean that numbers drop low, and then bounce again. What I do want to point out, however, is that Lantus dosing is based on the nadir -- the lowest number in the cycle. You raised Yuki's dose based on the pre-shot numbers. The 49 on 4/20 indicated that you need to reduce the dose. (You reduce if numbers fall below 50 in a cat that's within a year of diagnosis if you're using Tight Regulation and you reduce if numbers fall below 90 with SLGS.) Instead, you held the dose and then increased. In other words, you're giving Yuki too much insulin.