Fingerprints on the 2025 shelf

A new review is not a new permission. The five works filed here reached the desk between 2021 and 2025, and every card is citation-level. This is not a claim that each PDF was read to the last page. A percentage is used only as that paper stated it, under that paper's conditions. Erase the conditions and it stops being evidence.

More aircraft still do not make a city

The observable fact is this. Cavani, Iori, and Roberti, in Transportation Research Part C in 2021, pushed a tour of one truck and several drones to exact solutions. Their method, they report, solves instances of up to twenty-four customers to optimality, against earlier exact methods of a similar problem that reached about ten.

The inference can stay short. Twenty-four is how far their instances reached. It is not a city's orders at noon. Wind, an aging battery, and permission to fly over people are not at the center of that optimality. Read it beside Roberti and Ruthmair, who in the same year reached thirty-nine customers with one drone. Adding aircraft and enlarging the solvable instance are not the same sentence.

A green model is not a city meter

Chiang, Li, Shang, and Urban, in Applied Energy in 2019, cast last-mile drones as a mixed-integer green routing model and solved it with a genetic algorithm. Their computational results, they write, strongly support the claim that optimally routed drone delivery saves energy, carbon, and cost.

Do not mix an inference into that sentence. The result sits on their model and on their experimental instances. It is not a watt-hour metered on a street, and it is not an invoice. The conditions differ from Stolaroff, who warned about warehouses and distance, and from Kirschstein, who found drone-only delivery heavy in a dense city. Whoever averages the three papers into "drones are green" is wiping the fingerprints off the conditions.

What a survey can name is an open drawer

Benarbia and Kyamakya, in Sustainability in 2022, volume 14, article 360, surveyed the design of drone package-delivery systems. Routing, repositioning of charging stations, assignment, and e-commerce delivery sit in their keywords. What the paper promises is a map of approaches proposed up to that point, and lines of research still open. It is not a certificate that a flight is allowed in a given country this week.

Separate that role from Garg and colleagues' 55 studies, and from Jazairy and colleagues' 307 articles. Each count is the size of that review's own set. None of the three claims to have counted the papers of the world. When you cite a review, keep the years and the shelf of questions it actually read. A citation that erases the range is not a summary of the case. It is a sentence of advertising.

Seventy-one and 96.5 are quotations of a promise

Almodather Mohamed and Moataz Mohamed, in Drones, volume 9, issue 6, article 413, published on 6 June 2025, reviewed last-mile drones across seven domains: environment, economics, society, policy, routing, charging, and energy. The review states that the literature promises a 71 percent cut in emissions and a 96.5 percent cut in cost, compared with truck delivery.

The same abstract immediately qualifies the finding. Environmental and cost data vary. Two-dimensional models have limits. Experimental validation is missing. Therefore 71 and 96.5 are the review's summary of promises made by other studies, not an operator's measured result. The moment they are placed in a planning denominator, observation starts to dress itself as inference. This guide does not use those figures as a business case.

One hundred seventy-six is a cell in a matrix

G. Rohit, Ramesh Krishnan, and P. N. Ram Kumar wrote a systematic review and morphological analysis of drone last-mile delivery for IIM Kozhikode Society & Management Review. It was first published online on 22 April 2025. A volume may be dated 2026. The DOI 10.1177/22779752251329395 is enough to identify the paper. They set out seven dimensions and thirty-seven variants, and they report that a variance-intersection matrix marked 176 research gaps.

To read 176 as the number of questions the world does not yet know is a mistake. It is the number of cells in their combination of dimensions that they marked as not yet filled by the literature. Change the cut of the dimensions and the number of cells changes. A list of gaps is a candidate for the next drawer to open. It is not a complete inventory of reasons a flight cannot depart.